Dimorphism was detected in body length and in skull dimensions. The sample comprised 22 females and 14 males for which age was estimated. A single-phase Laird growth model was fitted to the body length/age data for females. Two curves were required for the males, one for those 4 GLGs old or younger and another for those older than 4 years. Male and female have about the same growth-rate until about age 4, after which males grow slower than females. Sexual dimorphism was also found in 9 external measurements, based on t-tests. Analysis of covariance showed that once the effect of body length was removed, only one of the 9 measurements, tip of upper jaw to genital aperture, was significantly different between males and females. Differences in skull measurements resulted mainly from an early slowdown in growth rate of longitudinal dimension in the male, before the slowing of increase in body length. Females and males could be sexed correctly by discriminant analysis with body length, condylobasal length and zygomatic width, and could also be correctly sexed with condylobasal length, width of rostrum at base and zygomatic width except for one young female. Eight skull length measurements were larger in adult females than in adult males after the effect of body length was removed, and five skull width measurements were larger in males when the effect of condylobasal length was removed. Asymmetry in the position of the blowhole and in skew of the skull is pronounced and is independent of body length and sex.