Background/Aims: To investigate the long-term efficacy and safety of two doses (33 and 67 µg/kg/day) of growth hormone (GH) in short Japanese children born small for gestational age (SGA). Methods: 96 children born SGA (age 3 to <8 years) were randomized to GH at 33 or 67 µg/kg/day for 104 weeks, or to an untreated control (UC) group for 52 weeks. After 52 weeks, the UC group was randomized to GH at a dose of 33 or 67 µg/kg/day for a 156-week extension study. Initial treatment groups continued unchanged for the extension phase. Efficacy was evaluated by change in height SDS for chronological age from baseline to 208/260 weeks. Results: After 208 weeks, change in height SDS from baseline (least square (LS) means (SE)) was 1.01 (0.47) and 1.99 (0.67) in the UC 33 and UC 67 µg/kg/day groups, respectively. After 260 weeks, change in height SDS from baseline was 1.22 (0.51) and 2.01 (0.64) in the 33 and 67 µg/kg/day groups, respectively. Insulin-like growth factor-1 levels were significantly higher in the groups receiving 67 µg/kg/day but largely remained within normal limits (–2 to +2 SDS). Conclusion: Long-term continuous GH treatment was well tolerated and effective in improving height SDS. Improvements were dose-dependent and significantly higher at 67 than 33 µg/kg/day.