The crystal structure of UCuPO was determined from single-crystal X-ray data and refined to a residual of R = 0.033 for 192 structure factors and 12 variables. It has a tetragonal ZrCuSiAs-type structure: P4/nmm, a = 379.3(1) pm, c = 823.3(2) pm, Z = 2. Magnetisation and magnetic susceptibility measurements of a powder sample in the range 5-300 K show UCuPO to order antiferromagnetically at T N = 220±2 K. Its χ(T) dependence appears to be highly anomalous with a strong upturn at low temperatures. The close relationship between UCuPO and U 2 Cu 2 P 3 O with respect to their crystal structures and their magnetic behaviour is discussed.