Ten polymorphic microsatellite DNA markers were employed to investigate population structure of the German cockroach, Blattella germanica, within and between apartments in a small city. Genetic differentiation at a range of spatial scales was quantified using F-statistics. No significant differentiation was found between German cockroaches in different rooms in the same apartment. Multiple apartments in separate buildings of an apartment complex were significantly differentiated and there was significant differentiation between multiple apartment complexes at distances of 3 km, however, tree-building methods did not cluster these apartments according to apartment complex. These results suggest that dispersal and gene flow occur freely within an apartment but that movement between buildings or between distant apartment complexes, which rely on human movement, is limited and that introduction from multiple sources may lie behind the diversity seen within complexes.