SETTING: Tuberculosis (TB) and human T-lymphotropic virus 1 (HTLV-1) are frequent in Peru. The prevalence of HTLV-1 among Peruvian TB patients is unknown. OBJECTIVE: To determine the prevalence of HTLV-1, HTLV-2 and the human immunodeficiency virus (HIV) in out-patients with TB and to compare HTLV-1-infected patients with seronegative patients. DESIGN: Cross-sectional study including subjects aged 18-65 years diagnosed with smear-positive pulmonary TB at health centres in northern Lima from November 2004 to August 2005. HTLV and HIV screening was performed using enzyme-linked immunosorbent assay; HTLV-1 and HTLV-2 were confirmed using line immunoassay. RESULTS: There were 311 participants with a median age of 29 years; 173 (56%) were men. HTLV-1 prevalence was 5.8% (18/311, 95%CI 3.2-8.4) and HIV prevalence was 1.3% (4/304, 95%CI 0.4-3.3). HTLV-2 was not diagnosed. In comparison with HIV- and HTLV-seronegative patients, HTLV-1-infected subjects were older (median age 44 vs. 28, P < 0.001) and were more likely to have been born in the southern Andes (OR 4.4, 95%CI 1.6-11.9). They were also more likely to report a history of TB deaths in the family (OR 5.4, 95%CI 1.7-16.8) and had more sputum smear results graded as 3+ (OR 4.1, 95%CI 1.5-11.2). CONCLUSION: HTLV-1 screening among Peruvian TB patients is important. Because 3+ sputum smears are frequent and mortality is high among relatives, families of HTLV-1/TB-positive cases merit special attention. © 2007 The Union.