BACKGROUND Osteogenesis imperfecta (OI) is a congenital disorder characterized by increased bone fragility and low bone mass. METHODS The presence of COL1A1 or COL1A2 mutation was investigated by direct sequencing in 72 patients with OI type I, III, or IV (27 males and 45 females; age range 0.2-62 years) from 37 unrelated families. The clinical features of these patients were also recorded. RESULTS Thirty-seven COL1A1 and COL1A2 mutations were identified, including 28 COL1A1 mutations and 9 COL1A2 mutations. Fifteen (41%) were novel mutations, and twelve (32%) were familial mutations. A review of their medical records revealed that the 72 patients could be classified into OI type I (n = 42), III (n = 5), and IV (n = 25). Twenty-nine patients had helical mutations (caused by the substitution of a glycine within the Gly-X-Y triplet domain of the triple helix), and 42 had haploinsufficiency mutations (caused by frameshift, nonsense, and splice-site mutations). Compared with haploinsufficiency, the patients with helical mutations had more severely impaired skeletal phenotypes, including shorter height, lower bone mineral density, poorer walking ability, more frequent manifestations of dentinogenesis imperfecta and scoliosis (p < 0.05). CONCLUSIONS Genotype and phenotype databases are expected to promote better genetic counseling and medical care of patients with OI.