Background: An 8-year era of interrupted indigenous measles transmission in Bulgaria came to an end in April 2009 when a large epidemic occurred that would eventually claim 24 253 cases and 24 deaths; infants, children and young adults of the Roma community were disproportionally affected. Compared with Western Europe, case-fatality rate and proportion of medical complications were uncharacteristically high. Methods: To disentangle underlying drivers of the outbreak and reasons for these medical complications, we assembled a number of national ecologic variables as well as regional individual-level data for 206 measles cases, randomly selected from national medical records. We conducted a logit regression analysis of data from individuals with medical complications. Results: Ecologic socio-economic predictors were not associated with measles cases by region, although the proportion of medical complications differed considerably. Individual-level data from a region with high medical complications revealed that mother’s education [odds ratio (OR) 0.79; 95% confidence interval (CI) 0.68–0.92], immunization status of the child (OR 0.28; 95% CI 0.08–0.94) and households declaring an income (OR 0.31; 95% CI 0.10–0.93) decreased the risk for developing severe medical complications such as pneumonia or encephalitis from a measles infection. Discussion: The extent of this outbreak with a high case-fatality rate and high proportion of medical complications calls for resolute public health action. We found vaccination and maternal education to be crucial conduits of curbing medical complications from measles infections. Ultimately, the goal is measles elimination in Europe by 2015, and these data hint at intervention entry points.