Geometric morphometric methods, minimizing redundancy and allowing more powerful statistical tests of shape differences, represent an appropriate tool for differentiation of seasonal populations or closely related taxa. To study seasonal dimorphism, samples of summer and winter populations of the codling moth, Cydia pomonella (L.) (Lepidoptera Tortricidae), were collected during 2003 and 2004 in two regions of Iran, Mianeh and Salmas. 101 and 99 forewings, and 72 and 88 hindwings were dissected from individuals of Mianeh and Salmas populations respectively. The alignment of stereoscopic images yielded a total of 15 landmarks on the forewings and 11 landmarks on the hindwings, and the geometric transformation resulted in 26 and 18 partial warp scores for the fore- and hindwings respectively. The multivariate analysis of variance based on these variables revealed significant differences among seasonal forms, geographic populations and sexes. Relative warp analysis showed a good discrimination between seasonal forms, especially when using hindwing landmarks in females. Overall shape deformations indicated that fore- and hindwings of both sexes were wider in the winter generation compared to that of summer, especially in females. It appears that a wider wing enables the winter form to fly better and thus, increase the dispersal range, particularly in overwintering females searching for suitable oviposition sites during spring. In both sexes the winter generation also had smaller forewings and larger hindwings compared with the summer form. The aerodynamic shape of the wing in the winter form enables the moths to cope better with unpredictable environmental conditions, like strong wind and heavy rain early in the season. Furthermore, adults of winter form are generally darker than the summer generation. This is a beneficially adaptive trait enabling better absorption of solar radiation during early spring.