Socioeconomic differences in breast cancer survival in the southeastern Netherlands between 1980 and 1989 were studied (n = 3928), as was the impact of prognostic factors (stage at diagnosis, morphology, and treatment) on such differences. An area-based measure of socioeconomic status (SES) in five groups, based on the postcode of residence at the time of diagnosis, was used. In univariate analyses the relative survival rate was used to correct for causes of death other than breast cancer. The measure of outcome in multivariate analyses was the hazard ratio. The results of both univariate and multivariate analyses suggested a small survival advantage for the higher SES groups. In a model with follow-up period, SES and age, the hazard ratios with 95% confidence intervals (CI) for SES groups from high to low were: 1.00, 1.06 (0.84-1.33), 1.04 (0.86-1.26), 1.15 (0.96-1.38), 1.18 (0.99-1.42). After a correction for stage at diagnosis, differences in survival were reduced substantially. Morphology and treatment were not important explanatory factors of the SES survival association. We conclude that small socioeconomic differences in breast cancer survival exist in The Netherlands and that stage at diagnosis is the most important determinant of such differences.