Genetic diversity and species delimitation were investigated among 39 isolates recovered from clinical and environmental sources in Central and South America, Africa, East Asia and Europe. All had been morphologically identified as Fonsecaea spp. Molecular analyses were based on sequences of the ribosomal internal transcribed spacers (ITS), -tubulin (TUB1) and actin (ACT1) regions. A phylogenetic approach using haplotype networks was used to evaluate species delimitation and genetic diversity. The presence and the modes of reproductive isolation were tested by measuring the index of differentiation (ID) and the index of association (IA). Based on the sequence data, the 39 Fonsecaea strains were classified into three major entities: (i) a group representing Fonsecaea pedrosoi, (ii) a second composed of F. monophora, and (iii) a third group including mostly strains from South America. The two major, clinically relevant Fonsecaea species, F. monophora and F. pedrosoi, also differed in the pathological symptoms found in patients. Moreover, F. pedrosoi is mostly recovered in clinical settings, whereas F. monophora is commonly isolated from the environment. One environmental strain with Fonsecaea-like appearance was shown to belong to a different species, only distantly related to the core-group of Fonsecaea.