Seven polymorphic microsatellite markers were used to analyze bollworm, Helicoverpa zea (Boddie), populations from various host plants in four locations in the southern United States. Linear distance between collection sites ranged from approximately 150 to 900 km. The analysis indicated low allelic range for all loci (2.286 ± 0.488 to 2.571 ± 0.787). Chi-square goodness-of-fit tests for deviation from Hardy-Weinberg equilibrium were not significant. Inbreeding coefficients, F_IS, were very variable among the seven loci with a bootstrapgenerated overall value of -0.104 ± 0.178 across all loci and populations. Overall population differentiation estimates, represented by F_ST, were essentially zero. In the analysis of variance of genotypes grouped into various geographical combinations, variation within individuals accounted for more than 93% of the total variation while no significant variation was detected between groups, among populations within groups, or among individuals within populations. The results indicated that extensive gene flow occurred between geographically distant bollworm populations, and the populations studied did not show any signs of differentiation based on the geographical location. Although there are no other microsatellite-based population studies for comparison, the results of the present study are congruent with the results of allozyme analyses on this species.