BMC Public Health 2009, 9:465 http://www.biomedcentral.com/1471-2458/9/465 Background As the developed world grapples with a proportionately high burden of non-communicable diseases (in this paper the term non-communicable diseases is used interchange- ably with chronic diseases) developing countries and countries undergoing socioeconomic transition are expe- riencing a mixed epidemic of non-communicable and communicable diseases [1]. In many developing coun- tries, research and investment in health has been mainly devoted to infectious diseases, despite the growing need to address chronic diseases with more effort and resources [2]. Deaths from infectious diseases, maternal and perina- tal conditions, and nutritional deficiencies combined are projected to decline by 3% over the next 10 years, while at the same time deaths due to chronic diseases are projected to increase by 17% [2]. As a result, it is estimated that of the projected 64 million deaths worldwide in 2015, 41 million (64%) will result from chronic diseases - unless urgent action is taken [2]. Obesity is a well recognized risk factor for various chronic health problems such as cardio- vascular diseases, hypertension, stroke, type 2 diabetes mellitus, osteoarthritis and certain cancers [3,4]. These conditions not only lead to reduced quality of life given their protracted nature, they also lead to premature death. Once associated only with high income countries, over- weight and obesity are now also prevalent in low and middle income countries [2,5]. Over the past several decades, the prevalence of obesity has been increasing both in developed and developing countries, and more noticeably in urban areas [6-8]. It is currently estimated that as much as 20-50% of urban pop- ulations in Africa are classified as either overweight or obese [9,10], and that by 2025 three quarters of the obese population worldwide will be in non-industrialized coun- tries [2]. Urbanization and socioeconomic transformation comes with increased access to energy-dense foods and less strenuous jobs resulting into many people having a positive energy balance and hence becoming overweight or obese [2,10-16]. Other factors that have been shown to be associated with a higher risk of overweight and obesity include genetic predisposition, metabolic disorders, gen- der and physical environmental factors among others [2,9,11-15]. While low socioeconomic economic status and poor neighborhoods have been associated with a higher prevalence of obesity and chronic diseases in devel- oped countries [17,18], studies in Africa have demon- strated by contrast a strong positive relationship between obesity and high socioeconomic status [14,19,20]. Addi- tionally very few studies have examined the changing dynamics of overweight/obesity and socio-economic sta- tus over time, making it difficult to assess the socioeco- nomic differentials in the rate of progression to overweight and obesity in urban Africa [21]. Despite being the least urbanized continent, Africa's pop- ulation is becoming increasingly urban and its cities are growing at unprecedented rates. Africa's urban population was 15 percent of the total population in 1950, and is pro- jected to exceed the fifty percent milestone by 2030 [22]. Rapid urbanization amidst poorly performing economies has resulted into a large proportion of urban residents being poor with limited access to social amenities [22,23]. In spite of rampant poverty in urban areas, access to cheap foods with a high content of fat and sugar among the urban poor is easier than among the rural population [24- 26]. Indeed some studies have shown that recent migrants to cities tend to have a higher body mass index (BMI) than rural residents and those with longer urban environment exposure [27]. With increasing urbanization, there might be a shift of the obesity burden to sections of the poor urban population who may not have the knowledge or financial resources to adopt healthier lifestyles [28-30]. Overall, poverty and social exclusion are likely to increase the risks of developing a chronic disease, but more impor- tantly the poor are also more likely to develop and die of complications of chronic diseases due to their inability to afford treatment and care [2,31]. The aim of this study is to shed light on the patterns of overweight and obesity in sub-Saharan Africa, with special interest in differences between the urban poor and the urban non-poor. The specific goals are to 1) describe changes in overweight and obesity among urban women in African countries; 2) examine how these changes vary by education and household wealth. Methods Data This paper used publicly available data from the Demo- graphic and Health Surveys by Measure DHS who approve and allow access to the data through their website. The surveys are designed to collect good quality, nationally representative data on demographic and health indicators and are carried out at regular intervals (usually every five years from the previous survey) in most developing coun- tries. The main aim of the DHS is to provide the much needed data on population and health situation in devel- oping countries. The repeat surveys help to provide indi- cators for monitoring goals set by countries and development agencies such as those set at International Conference on Population and Development (ICPD) in 1994 and the Millennium Development Goals (MDGs) set in 2000. We used data from all sub-Saharan African countries with a survey containing women's nutritional status conducted between 1992 and 1993 and another one carried out in 2003 or later. This criterion ensured that the estimates of changes over time, using survey-spe- cific sample weights, were based on a period of at least ten years between the two surveys. 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