National health systems are intended to provide equal access to health-care services to whole populations. However, they do not seem to address successfully the problem of social class differentials in access to health care, in particular access to preventive care. This study examines the relationship between the socioeconomic status (SES) of families and the use of preventive health care by children under a national health system in Spain. The study is based on weighted multivariate ordinal logistic regression analyses of data from the 1987 Spanish National Health Survey for a sample of 5,622 children, one to 10 years of age. A positive relationship was found between preventive health-care use by children and the SES of their families. Adult respondents' level of education and total family income were the most influential variables in this relationship. As these increased, children were more likely to receive visual, hearing, and dental exams. In addition, there was a gradient effect between family income and rate at which children received these preventive health-care services. Universal access to care, like that available in Spain, does not guarantee that social inequalities in children's receipt of preventive health care will not persist. In order to succeed, healthcare reform must deal with social issues beyond financial access to care.