Thirty-three patients attending the Nottingham Sports Injury Clinic in whom a clinical diagnosis of a stress fracture of the pars interarticularis was made were evaluated with both radiography and bone scintigraphy. This was done in an effort to distinguish a recent stress fracture which would produce a positive scintigram from an established 'incidental' spondylolysis giving a normal scintigram. Nine patients demonstrated abnormal radiography with a normal scintigram. A further nine patients had a positive scintigram. Six were associated with a spondylolysis indicating a recent stress fracture but two had normal radiography suggesting a stress fracture in the 'sub-radiological' phase. One patient had increased uptake in relation to degenerative changes of the lower lumbar facet joints. Oblique views of the scintigram helped in localisation of the abnormal uptake to the pars interarticularis.