BMC Public Health 2008, 8:136 http://www.biomedcentral.com/1471-2458/8/136 Background No other single age group sustains the negative health outcomes from their sexual behaviours as do adolescents 10 to 19 years of age [1]. Adolescents in Nigeria have high burden of sexual and reproductive health problems [2]: the age-specific fertility rate of adolescent girls was 126 per 1,000 in 2003; and a quarter of females aged 15–19 years had begun childbearing [3]. Adolescent girls contribute 55% of all clandestine abortions in the country [4]; and the national HIV sero-prevalence figure for age 15–19 years is 3.6% [5]. Early onset of sexual intercourse is associated with increased lifetime prevalence of sexual partners, thereby increasing the risk exposure to sexually transmitted dis- eases, including HIV/AIDS, and pregnancy. Early sexual debut also increases the risk of HPV infection, due to cer- vical immaturity; and thus the risk of cervical cancer increases [6]. Additionally, given the risk of pregnancy, early sexual initiators are less likely to complete their schooling thereby limiting their social and vocational futures. Empirical research, primarily from developed countries, indicates that the timing of sexual debut among adoles- cents is influenced by a wide range of factors including: age, gender, poverty, family structure, educational level, pubertal timing, socio-economic status, self-efficacy, peer influences, religiosity, knowledge and perceived risk of sexually transmitted infections, parenting practices and parental supervision, community, media and health ine- qualities [7,8]. Despite the high rates of early pregnancy and the associ- ated sequelae relating to early sexual debut in sub-Saharan Africa, to date there has been very little research that has explored the determinants or predictors of the timing of sexual intercourse among adolescents. Where it does exist, as Blum and Mmari note [9], the majority of studies has focused on the relationships between premarital sexual initiation and socio-demographic variables but rarely go beyond that. The current study aims to address this research gap. Specifically, the aim of the study is to deter- mine the predictors of age of sexual debut among a nationally representative sample of Nigerian adolescents. Methods Study Population and sampling The data for this study was obtained as part of the 2005 National HIV/AIDS and Reproductive Health Survey (NARHS). NARHS is a nationally representative house- hold survey of females (age 15–49 years) and males (age 15–64 years) of reproductive age. The primary objective of NARHS is to provide reproductive health information and data for monitoring the impact of reproductive health interventions. The study population was randomly selected using a three level, multi-stage method that aimed at selecting eligible people in each of the 36 states in Nigeria with equal prob- ability. Each state was first stratified by rural and urban areas, followed by random selection of enumeration areas, and subsequently individuals were selected at the household level. To increase the level of precision of the index obtainable at state level analysis, sample sizes in states with proportional allocation less than 250 were boosted to 250. Overall, the final sample allocated to each state was distributed proportionately by location (rural- urban) and gender. A sample of 10,258 individuals was originally drawn, of whom 10,081 participated (1.7% non-response rate). No significant gender difference was noted in the non- response rate. A total of 2,423 adolescents (15–19 years old) were included in the NARHS sample, consisting of 1,258 males (51.9%) and 1,165 females (48.1%). Among the males, 96.6% were never married compared to 75.9% among females (p < 0.001). Never-married adolescents (age 15–19 years) are the focus of this study. Of the 2,099 never-married adolescents in the NARHS sample, 29 did not provide relevant or valid information on sexual expe- rience or date of sexual debut and were excluded. Hence, the analytic sample for the study consisted of 2,070 never- married adolescents aged 15–19 years (1,195 males [57.7%] and 875 females [42.3%]). Data collection Data were obtained through structured interview that cov- ered various reproductive and sexual issues, including sex- ual behaviour, knowledge of HIV/AIDS and other sexually transmitted infections (STIs), condom perception and use, family planning (FP) attitudes and utilisation, gen- der-based violence, safe motherhood and communica- tion. The questions were largely derived from UNAIDS general population HIV/AIDS indicator questionnaire [10] and the Nigeria Demographic Health Survey (NDHS) [3]. Questionnaires were primarily in English – the official language of the country – due to the linguistic complexity of Nigeria (with over 250 local languages); however, for each selected community, key words/phrases were trans- lated into the local language(s). A similar approach was used successfully in the 2002 Youth Behavioural Surveil- lance Survey and the 2003 NARHS. Data collection was carried out using trained interviewers, under the supervision of an independent research agency that worked closely with officials of State Ministry of Page 2 of 14 (page number not for citation purposes)