Trilostane is used to treat dogs with pituitary-dependent hyperadrenocorticism (PDH). In our institution, it was initially dosed based on bodyweight (BW) categories, since April 06 it is dosed per kg BW. Our objectives were to compare effectiveness, number of dose adjustments and side effects of the two dose regimens in dogs with PDH. Dogs of group 1 (28 dogs) received trilostane based on BW categories (< 5 kg, 30 mg; 5 - 20 kg, 60 mg and > 20 kg, 120 mg; SID); dogs of group 2 (20 dogs) received 2 - 5 mg/kg SID. Treatment goal was a post-ACTH cortisol of 1 - 2.5 and 1.5 - 5.4 µg/dl in group 1 and 2, respectively. Starting doses were significantly higher in group 1 and stayed higher until re-check at 4 - 7 months. Baseline and post-ACTH cortisol were significantly decreased compared to pre-treatment at all time points in both groups. Significantly more dogs of group 2 (5/20) needed a dose increase at the first re-check and significantly more dogs of group 1 (10/23) a dose reduction at the last re-check. Intermittent discontinuation was necessary in 25 and 10 % of dogs of group 1 and 2, respectively. We conclude that dosing per kg BW results in comparable clinical improvement, decrease in cortisol, but lower risk of side effects.