Background: Physical inactivity is more prevalent among racial and ethnic minorities than among Caucasians. It is not known if differences in participation in leisure time physical activity are due to differences in social class. Thus, this paper provides estimates of the prevalence of physical inactivity during leisure time and its relationship to race/ethnicity and social class. Methods: This was a national representative cross-sectional survey with an in-person interview and medical examination. Between 1988 and 1994, 18,885 adults aged 20 or older responded to the household adult and family questionnaires as part of the Third National Health and Nutrition Examination Survey . Mexican-Americans and African-Americans were over-sampled to produce reliable estimates for these groups. Multiple assessment of social class included education, family income, occupation, poverty status, employment status, and marital status. Results: The age-adjusted prevalence (per 100) of adults reporting leisure time inactivity is lower among Caucasians (18%) than among African-Americans (35%) and Mexican-Americans (40%). African-American and Mexican-American men and women reported higher prevalence of leisure time inactivity than their Caucasian counterparts across almost every variable, including education, family income, occupation, employment, poverty and marital status. Conclusions: Current indicators of social class do not seem to explain the higher prevalence of physical inactivity during leisure time among African-American and Mexican-American. More research is needed to examine the effect of other constructs of social class such as acculturation, safety, social support and environmental barriers in promoting successful interventions to increase physical activity in these populations.