Deoxyuridine 5'-triphosphate nucleotidohydrolase from Mason-Pfizer monkey retrovirus (M-PMV dUTPase) is a betaretroviral member of the dUTPase enzyme family. In the mature M-PMV virion, this enzyme is present as the C-terminal domain of the fusion protein nucleocapsid-dUTPase. The homotrimeric organization characteristic of dUTPases is retained in this bifunctional fusion protein. The fusion protein supposedly plays a role in adequate localization of dUTPase activity in the vicinity of nucleic acids during reverse transcription and integration. Here, the nucleocapsid-free dUTPase (48 426 Da) was cocrystallized with a dUTP substrate analogue using the hanging-drop vapour-diffusion method. The obtained crystals belong to the primitive hexagonal space group P6(3), with unit-cell parameters a = 60.6, b = 60.6, c = 63.6 angstroms, alpha = 90, beta = 90, gamma = 120 degrees. Native and PtCl4-derivative data sets were collected using synchrotron radiation to 1.75 and 2.3 angstroms, respectively. Phasing was successfully performed by isomorphous replacement combined with anomalous scattering.