A substantial proportion of patients who have undergone a radical prostatectomy for localised prostate cancer will have either persistently detectable prostate-specific antigen (PSA) levels or a delayed rise in PSA. The optimum treatment for these situations is not known. The key question is whether the PSA is reflective of local or distant progression. For salvage radiotherapy to be most effective, treatment should be considered before the PSA level is allowed to rise too high, when disease is more likely to be confined to the prostate bed. However, at low PSA levels, current imaging techniques are poor at detecting disease, making it difficult to differentiate local and distant recurrences and to target the radiotherapy appropriately. We review current and investigational imaging techniques, including bone scan, computed tomography, magnetic resonance imaging, positron emission tomography and Prostascint, assessing their utility in the situation of biochemical recurrence after radical prostatectomy.