Poverty and other socio-environmental determinants may contribute to the occurrence of leprosy. However, there is no previous evidence on the effectiveness of cash transfer programmes in reducing leprosy case detection among children under 15 years old. Objective: This study aimed to assess the effect of the Brazilian conditional cash transfer programme (Bolsa Famı´lia Programme, BFP) on the reduction of new case detection rates (NCDR) of leprosy in Brazilians under 15 years old. Methods: We performed a mixed ecological study with the Brazilian municipalities as units of analysis, during 2004–2015. The main independent variables were: BFP coverage of target population (poor and extremely poor families) and BFP coverage of the total population of the municipalities. Data were obtained from public databases. We included 1,120 (of 5,570) municipalities in the analysis, using fixedeffects negative binomial models for panel data, adjusted for the municipal coverages of the Brazilian primary health care programme (Family Health Strategy, FHS) and for a set of sociodemographic covariates. Results: We found an increasing trend in the median BFP coverages and a decreasing trend in the NCDR of leprosy in individuals under 15 years old. This indicator was significantly reduced in municipalities with higher BFP coverages of target population (RR ¼ 0·75; CI 95% 0·63–0·88) and higher BFP coverages of the total population of the municipalities (RR ¼ 0·85; CI 95% 0·79–0·93). Conclusions: During the study period, BFP was associated with a reduction of the NCDR of leprosy among Brazilians aged less than 15 years old, living in municipalities with a high risk of leprosy transmission.