The purposes of this study were to measure incidence and determine risk factors associated with opportunistic infections (OIs) and mortality among an HIV-infected cohort in Nairobi, Kenya. Three hundred and eighty-one seropositive ambulatory adults in Nairobi, Kenya were followed from 1997 to 2000 with participants visiting the clinic every two months and when acutely ill. Acute bronchitis was the most frequent diagnosis, followed by sexually transmitted infections, candida vaginitis (among women), fever, diarrhoea, pneumonia, HIV-associated skin rash, oral candidiasis and urinary tract infection. Associations between the frequency of these diagnoses including survival and sociodemographic factors and initial CD4 count were assessed. A CD4 count <200 cells/mL at recruitment was strongly associated with decreased survival (adjusted odds ratio=3.0, 95% confidence interval 1.7-5.1). These findings may help to target high-risk populations and guide OI prevention and treatment strategies including decisions regarding initiation of antiretroviral therapy in sub-Saharan Africa.