The concept that clefting is associated with diminished height and weight was examined in a cross-sectional sample of 45 pairs of twins discordant for cleft of the lip and/or palate from three to 17 years of age. Contrary to expectation, a remarkable similarity between cleft and non-cleft twins was found from three to 10 years of age. It was only from 10 to 17 years of age that the expected diminution in height and weight was observed. Average heights and weights at two-year intervals were compared with population norms for the age range in question for cleft and non-cleft twins. For both height and weight, the "over 10" decrease below the population norms was attributable to the DZ cleft twins. The MZ cleft twins remained very close to the norms while their non-cleft matched siblings exceeded the norm after 10 years of age. In addition, the decreased weight for cleft twins was seen to occur earlier for girls than for boys, suggesting a relationship with the onset of puberty. This was not seen for height. It is, therefore, proposed that the endocrine controls of maturation at puberty are linked in some fashion to cleft of the lip and/or palate.