Cytochrome P450 enzymes constitute a large family of haemoproteins that catalyze the monooxygenation of a great variety of endogenous and exogenous organic compounds. Cytochrome P450 203A1 (CYP203A1, RPA1009) from the metabolically versatile organism Rhodopseudomonas palustris binds a broad range of substrates, in particular substituted aromatic compounds. Crystals of CYP203A1 suitable for X-ray crystallography have been obtained and diffraction data were collected in-house to 2.0 A resolution from a single crystal. The crystals belong to space group P222, with unit-cell parameters a = 40.1, b = 95.1, c = 99.0 A, alpha = beta = gamma = 90 degrees. There is one protein molecule per asymmetric unit.