Territoriality in the flesh fly, Sarcophaga crassipalpis (Diptera: Sarcophagidae) was studied in the laboratory. In rectangular enclosures, male flies exhibited a lower tolerance (occupation of the same physical space) of same-sex conspecifics than did female flies. In circular arenas, male flies showed significantly higher levels of spatial separation among themselves (as determined from nearest neighbor analyses) than did females: males were distributed uniformly whereas females were nearly random. The male spatial behavior occurred during the photophase but not the scotophase of light-dark cycles, suggesting that visual cues are required for maintenance of inter-individual spacing. No significant differences in male spacing behavior occurred between subjective day and subjective night in either constant dark or constant light conditions, suggesting that spatial patterning is not driven by a circadian rhythm.