BACKGROUND: Social class is an important aspect of all societies. Social class differences in the prevalence of common mental disorder are likey to vary according to time, culture and stage of economic development. The present study aimed to investigate the intermediaries between social class and common mental disorder in a deprived area of Northeast Brazil. The Self Reporting Questionnaire (SRQ) was used to estimate the prevalence of common metnal disorder. METHOD: A cross-sectional survey was conducted of 683 adults, aged 15 yeas and over, living in a random sample of private households in area II of Olinda, Recife Metropolitan Region, Pernambuco, Brazil. RESULTS: Poor education (odds ration, OR 2.5, 95% CI 1.2-5.2; 5 years vs or = 11 years education) and low income (OR 2.4, 95% CI 1.0-5.6; or = 1/4 minimum wage vs 1 minimum wage) were independently associated with the prevalence of common mental disorder. Univariate associations with occupation, housing conditions and possession of household apliances could be understood in part by thier association with poor education. CONCLUSIONS: Brazil has the second most unequal distribuition of income in the world. Disparity in education attainment could be one of the most important factors perpetuating social inequalities in psychiatric disorder in the country.