In 78 consecutive patients, we performed fine-needle aspiration of the hip before revision surgery. At the revision operation biopsies were taken from the capsule and joint tissues. The aspirate and the homogenised soft-tissue specimens were cultured using a radiometric technique. Fifteen hips proved to be infected and 63 sterile on culture of the tissues taken during revision surgery; 94% of the aspiration results were correct. The sensitivity of the technique was 87% and the specificity 95%. Fine-needle aspiration combined with a radiometric culture technique is a simple and reliable method of diagnosing infection of hip prostheses.