A study was undertaken to determine the rate of population expansion of an ischnoceran Phthiraptera, Goniocotes gallinae (infesting the domestic fowl, Gallus gallus domesticus), on the basis of in vitro and in vivo studies. Data obtained from in vitro rearing were utilized to construct the life history of the louse. The values of the gross reproductive rate (12.49 female eggs/female), net reproductive rate (8.31 female eggs/female), mean length of generation (36.91 days), precise generation time (35.65 days), finite rate of increase (1.06 female/days), and intrinsic rate of natural increase (0.059) of G. gallinae were determined. However, doubling-time values recorded during in vivo studies (14 days) was comparatively higher than those during in vitro rearing (11.73 days).