In total hip arthroplasty (THA) Technetium scintigraphy can help to diagnose a loose implant by detecting elevated osteoblastic activity. It has been used for timing the revision of cemented implants. In uncemented cups progressive radiological acetabular osteolysis can be present before loosening accurs, but it is probably unwise to await cup loosening before embarking on revision. We explored the possible relationship between such osteolysis and positive findings on technetium scintigraphy, to see if the technique could predict the need for revision. Between 1990 and 1996 500 hydroxyapatite-coated hip prostheses were implanted (follow-up range: 9-15 years), and technetium scintigraphy and plain radiography were performed annually postoperatively. 32 cups were revised for progressive acetabular osteolysis. We compared the introperative findings at revision with the pre-operative scintigraphic and radiographic results. The sensitivity and specificity for diagnosing progressive acetabular osteolysis by technetium scintigraphy were 34% and 0% respectively. The sensitivity and specificity of the technique for detecting loosening were 38% and 73% respectively. The sensitivity and specificity of technetium scintigraphy for detection of a either loosening or progressive acetabular osteolysis are worse than reported for plain radiography. Despite negative scintigraphy, there may be progressive bone loss at a critical level. Scintigraphy has no additional value to plain radiography as a reliable indicator for timing cup revision in the process of progressive acetabular osteolysis.