The effects of chronic growth hormone (GH) deficiency on muscle size and strength of postural (quadriceps) and non-postural (hand-grip) muscle groups, as well as on vertical jump capacity, were evaluated in six adults with childhood-onset GH deficiency. Data obtained were compared to those recorded in an age-, sex- and exercise-matched healthy control group. Thigh muscle plus bone cross-sectional area (CSAM+B) of the dominant quadriceps was significantly lower (p < 0.001) than in controls, while the CSAM+B/(Body height)2 ratio was similar to that of controls. The maximum voluntary contraction (MVC) of the quadriceps of patients was significantly lower (p < 0.002) than in controls, while no differences existed in the quadriceps force expressed per unit area (MVC/CSA) between patients and controls. As far as hand-grip was concerned, the CSAM+B of the dominant forearm was significantly lower (p < 0.003) than in controls, while the CSAM+B/(Body height)2 ratio was no different. The hand-grip MVC of patients was significantly lower (p < 0.004) than in controls, while no differences existed in the MVC/CSA ratio. It is noteworthy also that no difference existed in the hand-grip to quadriceps MVC ratio of the two groups. Furthermore, no differences were found in the vertical jump capacity, because both delta Height and delta Height/Body weight of patients were not significantly different from those of controls. In conclusion, our study suggests that GH deficiency seems to reduce the size and strength of postural and non-postural muscle groups to the same extent.(ABSTRACT TRUNCATED AT 250 WORDS)