We estimated the level of under-reporting of visceral leishmaniasis (VL) cases by comparing the actual reported cases with those expected as estimated using age- and sex-stratified incidence proportions obtained in a cohort of 31,324 persons. The average incidence proportion of VL cases in study population was 5.7/1,000 (95% confidence interval [CI] = 4.88-6.54) and 1.09/1,000 persons (95% CI = 0.99-1.20) based on the reported cases in two primary health centers. The overall magnitude of VL cases not reported to the government agencies was higher by a factor 4.17 (95% CI = 3.75-4.63) than for reported cases. The levels of under-reporting were 4.74 (95% CI = 4.11-5.47) in males and 3.51 (95% CI = 2.99-4.11) in females with no significant difference (P > 0.05). It was significantly higher in persons >or= 30 years of age than in persons 30 years of age (P < 0.05).