OBJECTIVE: To evaluate the relationship between serum total homocysteine levels and retinopathy of prematurity (ROP). METHODS: This prospective case-control study involved premature infants diagnosed with ROP 4 weeks after birth (cases); controls were premature infants not developing ROP during follow-up. Fasting serum total homocysteine concentrations were determined in all participants 4 weeks after birth, using high performance liquid chromatography. RESULTS: A total of 45 and 35 infants were included in the case and control groups, respectively. The mean +/- SD (range) serum total homocysteine levels were 10.36 +/- 1.72 mu mol/l (7.45 - 14.84) in infants with ROP and 8.41 +/- 2.12 mu mol/l (5.56 - 13.90) in controls. This difference was statistically significant. Mean +/- SD total homocysteine levels were higher in infants with more severe ROP (11.45 +/- 1.76 mu mol/l) compared with mild ROP (9.92 +/- 1.56 mu mol/l). CONCLUSIONS: Elevated serum total homocysteine levels are associated with the development of ROP in premature infants. Further studies with larger patient populations are required, to improve understanding of the relationship between homocysteine and ROP development.