Poor mental health accounts for considerable disease burden among young people globally. We investigated the prevalence and determinants of affective disorders among rural Zimbabwean youth in 2006. We undertook a cross-sectional survey among 1495 Zimbabwean youth aged 15-23 (median 18) from 12 rural communities in three provinces in south-eastern Zimbabwe. Mental health was assessed using the Shona Symptom Questionnaire (SSQ), a locally validated 14-item indigenous screening tool for affective disorders, notably depression and anxiety disorders. Participants scoring >or=8/14 were considered at risk of being affected and >or=11 as at risk of being severely affected. Most participants (93.1%) completed the SSQ. Of these, 51.7% (95%CI:49.0-54.3%) scored >or=8/14 and 23.8% (95%CI:21.5-26.0%) scored >or=11. Affective disorders were independently associated with household poverty (adjusted odds ratio (AOR) 1.9, 95%CI:1.4-2.7), living in a female-headed household (AOR 1.3, 95%CI:1.0-1.7), having moved home within last 5 years (AOR 1.4, 95%CI:1.0-1.9) and feeling stigmatized (AOR being shunned by others 3.7, 95%CI:2.5-5.7). There was a strong linear association between risk of affective disorders and sexual risk taking (ever sex AOR 1.5, 95%CI:1.0-2.4, and 2.8, 95%CI:1.9-4.2 for affected and severely affected, respectively, test for trend P < 0.001; >or=2 lifetime partners AOR 2.3, 95%CI:1.1-4.8 and 5.4, 95%CI:2.7-10.7, test for trend P < 0.001). This study indicates high levels of psychological morbidity among rural Zimbabwean youth which was associated with sexual risk taking. Interventions to prevent, identify and treat mental health disorders in this vulnerable population are urgently required. In HIV-endemic countries, such interventions may also help reduce HIV transmission.