This study investigated the effects of ovariohysterectomy performed at 10 weeks of age on body weight, behaviour, bone length, serum calcium and phosphorus concentrations and gonadal hormone (progesterone and oestradiol) levels until 24 weeks of age in 31 clinically healthy mixed-breed female puppies. The littermates were randomly assigned to three groups. Group I (n = 11) was completely ovariohysterectomised, Group 11 (n = 10) was incompletely ovariohysterectomised with one ovary left intact, and Group III (n = 10) was sham operated. No significant differences were found between the groups for any of the parameters evaluated. It was determined that, except for two measurements of two animals in Group 11 at 20 and 24 weeks of age, all animals had undetectable concentrations of oestradiol 17-beta. These findings suggest that an ovariohysterectomy performed on a mixed-breed dog at 10 weeks of age does not affect her skeletal, behavioural or physical development in the period studied, i.e. until 24 weeks of age.