The SH3 domain of human AHI1 was cloned and expressed in Escherichia coli. The protein was purified by affinity and size-exclusion chromatography and was crystallized using the sitting-drop vapour-diffusion method at 293 K. A complete data set was collected to 2.5 A ° resolution at 110 K. The crystal belonged to space group P41212, with unit-cell parameters a = 67.377, b = 67.377, c = 98.549 A ° .