['To determine impediments to the effective reduction of maternal-infant transmission of HIV in the municipality of Campos dos Goytacazes, RJ, Brazil.', 'This is a cohort study, with medical follow-up, of pregnant women with confirmed diagnosis of HIV infection, and their infant children, assisted at the Municipal Specialized Service of Sexually Transmitted Diseases/AIDS from January 2004 to April 2007. Information regarding exposure and outcome variables was collected from their medical records. Frequencies of variables were determined and bivariate analysis performed for exposure factors and transmission of HIV. Relative risks of HIV transmission associated with exposure variables were calculated using 95% confidence intervals. Statistical significance of risk associations was evaluated.', 'Seventy-eight mother-child pairs were studied; the rate of maternal-infant transmission of HIV was 7.7%. Variables showing significant association with maternal-infant transmission of HIV were the non-utilization of antiretrovirals for prophylaxis or treatment during pregnancy (RR = 21.00; 95%CI 2.64-166.74, p = 0.001) and diagnosis of maternal disease after pregnancy (RR = 6.80; 95%CI 1.59-29.17, p = 0.025). New pregnancies in women with other children also exposed to HIV occurred in 19.12% (15/78) of cases.'] Do persistent operational challenges lead to non-reduction in maternal-infant transmission of HIV?