To evaluate socioeconomic inequalities and its relation to infant mortality in Bolivia's municipalities in 2001.An ecological study based on data from the 2001 National Census on Population and Housing (Censo Nacional de Población y Vivienda) covering the 327 municipalities in Bolivia's nine departments. The dependent variable was the infant mortality rate (IMR); the independent variables were indirect socioeconomic indicators (the percentage of illiterates older than 15 years of age, and the building materials and sanitation features of the houses). The geographic distribution of each indicator was determined and the associations between IMR and each socioeconomic indicator were calculate using Spearman's rank correlation coefficient and adjusted with Poisson regression models.The resulting IMR for Bolivia in 2001 was 67 per 1000 live births. Rates ranged from <0.1 per 1000 live births in the Magdalena municipality, Beni department, to 170.0 per 1000 live births in the Caripuyo municipality, Potosí department. The mean rate of illiteracy per municipality was 17.5%; the mean percentage of houses without running water was 90.4%, and for those lacking sanitation services, 67.6%. The IMR was inversely associated with all of the socioeconomic indicators studied. The highest relative risk was found in housing without sanitation services. Multifactorial models adjusted for illiteracy showed that the following indicators were still strongly associated with the IMR: no sanitation services (Relative risk (RR)=1.54; 95% Confidence Interval (95%CI)=1.38-1.66); adobe, stone, or mud walls (RR=1.54; 95%CI: 1.43-1.67); and, corrugated metal, straw, or palm branch roof (RR=1.34; 95%CI: 1.26-1.43).A significant association was found between poor socioeconomic status and high IMR in Bolivia's municipalities in 2001. The municipalities in the country's central and southeastern areas had lower socioeconomic status and higher IMR. The lack of education, absence of basic sanitation, and precarious housing conditions were key factors that tripled the risk of death.