Although somatostatin analogues are effective medical therapy for acromegaly, the serum insulin-like growth factor-I (IGF-I) levels remain uncontrolled in 35% of patients. Combined therapy with octreotide LAR and cabergoline has been reported to normalize IGF-I levels in 42-56% of Caucasian patients with acromegaly. However, it remains to be clarified whether combination therapy is effective in Japanese patients and on tumor shrinkage. We conducted a retrospective study on combined therapy in patients with octreotide-resistant acromegaly. Ten patients with acromegaly who showed octreotide-resistance were enrolled in this study. Cabergoline was added in doses of 0.25-2.0mg/week. Serum GH and IGF-I levels and tumor volume were assessed before and after treatment, and factors correlated with effect of the combined therapy were analyzed. Although serum GH levels did not decrease, serum IGF-I levels significantly decreased by 20% after 6 months of combined therapy compared with baseline (p < 0.05). As a result, serum IGF-I levels normalized in 30% of the patients. Tumor volume after combined therapy also significantly decreased (p < 0.01). There were no correlations between the decrease of serum IGF-I levels during combined therapy and the response of GH in a bromocriptine test, random GH, IGF-I, and PRL levels, the tumor volume, and the expression of PRL and dopamine D2 receptor in the tumor. In conclusion, we demonstrated that the addition of cabergoline to octreotide LAR is a beneficial option in Japanese patients with octreotide-resistant acromegaly, irrespective of serum PRL levels and the response of GH levels in a bromocriptine test.