This study sought to examine the effects of inbreeding on physical development and fluctuating asymmetry (FA). A total 144 male high-school students (mean age = 18.11 +/- 0.52) whose parents are first cousins (F = 0.125) of low-socioeconomic status and 146 male students (mean age = 18.08 +/- 0.54) from the same school who do not have any consanguineous parents (F = 0) were observed in Ankara. In addition to the weight and height measurements of the individuals, eight bilateral traits (hand width, elbow width, wrist width, knee width, ankle width, foot width, ear length, and ear width) were measured. Whereas the inbred group has lower values in terms of weight and height, the difference in body mass index between the groups is not significant. Although the inbred group is more asymmetric in terms of the observed bilateral traits, the differences are below the significance level. However, the composite FA index shows that the inbred group is more asymmetric and the difference is significant (P < 0.05). Inbreeding depression has a negative effect on weight and height development, and a negative effect on developmental stability. Am. J. Hum. Biol. 22:557-562, 2010. (C)2010 Wiley-Liss, Inc.