Rosuvastatin is a new statin that has been shown to produce substantial dose-dependent reductions in low-density lipoprotein cholesterol (LDL-C) in Western and Japanese hypercholesterolemic patients. Rosuvastatin efficacy and safety were assessed in an open-label, dose-titration trial of 37 Japanese patients with heterozygous familial hypercholesterolemia. After an 8-week dietary lead-in period, patients received rosuvastatin on the following schedule: 10 mg/day during weeks 0-6; 20 mg/day during weeks 6-12, and 40 mg/day for weeks 12-18. Mean percentage reductions from baseline in LDL-C (49.2-56.7%), total cholesterol (39.4-45.4%), and non-high-density lipoprotein cholesterol (non-HDL-C) (46.7-54.3%) were highly significant at each dose (p < 0.0001). Similar significant reductions in triglycerides (18.2-25.0%; p < 0.006) and increases in HDL-C (9.6-13.6%; p < 0.005) were observed. Rosuvastatin was well tolerated. Two patients withdrew from the study because of adverse events unrelated to the study treatment. No patients had clinically significant elevations in liver transaminases. Two patients exhibited a single increase in creatine kinase (one unrelated to study treatment, the other possibly related) with no muscle symptoms. Rosuvastatin produced significant beneficial changes in all lipid parameters in Japanese patients with heterozygous familial hypercholesterolemia and was well tolerated.