BACKGROUND: Several particular aspects of diversity patterns of Chilean littoral fishes are still poorly understood, and existing studies within this scope are fundamentally based on bibliographic compilations. In this study, we use empirical data to assess whether the diversity patterns of fish fauna along 4000 km of the Chilean coast (20° - 55° S)can be explained in relation to the environmental latitudinal gradient. Fish were collected from intertidal pools and subtidal habitats (<35 m). Analyses focused on the spatial scales of diversity patterns and latitudinal breaks in species diversity, comparing the observed patterns among intertidal and subtidal habitats. Correlations between variance in environmental factors and species richness were calculated. RESULTS: Richness was positively autocorrelated at spatial scales <1000 km. Overall, richness was observed to progressively decrease toward higher latitudes, but values for intertidal fish in particular decreased towards the north and south from the point of maximum richness. This is a pattern that has already been recorded for other intertidal organisms. Similarity was seen to decrease with distance, and turnover point for intertidal fishes was high around 30° - 32° S, while northern species disappeared between 36° - 39° S. Subtidally, there is an invasion of subantarctic species between 53° - 55° S. CONCLUSIONS: Environmental variables are significant to the diversity patterns recorded. However, richness variations could result from many types of variables acting together and not from one single factor.