This review deals with the differences between Drosophila melanogaster and Drosophila simulans in their mitotic and polytene chromosomes. The description of the mitotic karyotypes of D. melanogaster and D. simulans is mainly based on the methods that allow to differentiate their euchromatin from their heterochromatin: banding patterns, distribution of satellite DNAs and location of the rDNA. The polytene chromosomes karyotypes are known for many years to differ by a major paracentric inversion on chromosome 3 and minor few differences. The main difference take place in their chromosomal polymorphism: D. melanogaster is highly polymorphic while D. simulans has long been known to be a monomorphic species. In fact, despite worldwide studies of natural populations for both species, only 14 unique inversions have been described for D. simulans while more than 500 inversions are already known for D. melanogaster.