A survey is made of the overall pattern of distribution of freshwater fish within Malaya and also of the associations found in the three important habitat types. The lack of east—west differentiation indicates that geographical barriers are not important in determining the distributional pattern. A marked north—south differentiation probably reflects edaphic and climatic factors. Analyses based on constancy are given for the fish associations of blackwaters, ordinary streams in tree country, and riceland habitats. Each has a distinctive fish association with a relatively small number of frequent species. Blackwater associations can be divided into subassociations corresponding to different types of blackwaters. Tree country and riceland associations show some regional differentiation. The tree country association is remarkably diversified and appears to be a true association, not a fortuitous assemblage of species with similar tolerances. Adverse factors such as low oxygen and low pH probably restrict the associations found in blackwaters and ricelands. These contain both specialist and generally tolerant species, the latter becoming more important the more extreme the habitat. The riceland fauna is depauperate as compared with neighboring countries, and there are possibly vacant ecological niches.