The enzyme nicotinic acid mononucleotide adenylyltransferase (NaMN AT; EC 2.7.7.18) is essential for the synthesis of nicotinamide adenine dinucleotide and is a potential target for antibiotics. It catalyzes the transfer of an adenyl group from ATP to nicotinic acid mononucleotide to form nicotinic acid adenine dinucleotide. NaMN AT from Pseudomonas aeruginosa was overexpressed in Escherichia coli and crystallized at 291 K using 100 mM bis-Tris propane pH 7.0, 700 mM trisodium citrate and 15%(v/v) glycerol. X-ray diffraction data have been collected to 1.70 A. The crystals are tetragonal, belonging to space group P4(1)22 (or P4(3)22), with unit-cell parameters a = b = 65.02, c = 109.80 A. The presence of one monomer in the asymmetric unit gives a reasonable V(M) of 2.15 A(3) Da(-1), with a solvent content of 42.7%.