BackgroundThere is a lack of evidence regarding chronic disease modifiable risk factors among prisoner populations in Latin America. The purpose of this study was to estimate the prevalence of modifiable risk factors for chronic diseases and to assess their relationship with length of incarceration.MethodsWe analysed data from a cross sectional study in which 4241 prisoners were randomly selected to answer a questionnaire with socio-demographic and health behaviour content using an audio computer-assisted self-interview format. Physical activity (PA), low-quality diet, current smoking and alcohol or cocaine use during the last month in prison were our main outcomes. Quantile regression models and logistic regression models were performed.ResultsOur final analytical sample consisted of 3774 prisoners from four Mexico City prisons. PA was estimated as 579 median metabolic equivalents-min/week, prevalence of alcohol use was 23.4%, cocaine use was 24.2% and current smoking was 53.2%. Our results suggest that, as length of incarceration increased, PA as well as alcohol and cocaine use increased, whereas the quality of diet decreased.ConclusionThis study supports the hypothesis that exposure to prison environment (measured by length of incarceration) fosters modifiable risk factors for chronic diseases, particularly diet quality and cocaine use.