A complex of the periplasmic chaperone FimC and the mannose-binding adhesin FimH from the Escherichia coli type 1 pilus system has been crystallized from ammonium sulfate solution using the hanging-drop vapour-diffusion method. The crystals diffract to a minimum Bragg spacing of 2.7 A and belong to the space group P4(1)2(1)2 or P4(3)2(1)2 with cell dimensions a = b = 97.7, c = 215.9 A at room temperature. Data to 3.0 A have been collected from a single-crystal frozen to T = 100 K.