Penicillin acylase proteins are amidohydrolase enzymes that cleave penicillins at the amide bond connecting the side chain to their beta-lactam nucleus. An unannotated protein from Bacillus subtilis has been expressed in Escherichia coli, purified and confirmed to possess penicillin V acylase activity. The protein was crystallized using the hanging-drop vapour-diffusion method from a solution containing 4 M sodium formate in 100 mM Tris-HCl buffer pH 8.2. Diffraction data were collected under cryogenic conditions to a spacing of 2.5 A. The crystals belonged to the orthorhombic space group C222(1), with unit-cell parameters a = 111.0, b = 308.0, c = 56.0 A. The estimated Matthews coefficient was 3.23 A3 Da(-1), corresponding to 62% solvent content. The structure has been solved using molecular-replacement methods with B. sphaericus penicillin V acylase (PDB code 2pva) as the search model.