OBJECTIVE To assess whether vascular and other retroperitoneal anomalies are more frequent during retroperitoneal lymph node dissection (RPLND) for metastatic testicular tumours (when retroperitoneal masses persist after chemotherapy) than would be expected, based on the initial observations from one centre with a large experience of RPLND in the UK. METHODS A prospective series of 278 consecutive patients treated with RPLND for testicular tumours comprised the sample population. For each patient the presence or absence of four factors from the history was recorded. Each patient then underwent RPLND. During surgery, a template was constructed of the anatomy of the retroperitoneum and the information stored. Eight different retroperitoneal anatomical anomalies were identified in the sample population; the incidence of each was then compared with the largest available study of a normal population, and differences analysed statistically. RESULTS Of the 278 patients who had RPLND, 55 had 59 anomalies (21%), found by history and as retroperitoneal vascular and urological anomalies; cryptorchidism was present in 7.6%, 9.5 times the incidence in the control population (P < 0.01). A left-sided inferior vena cava was present in 3.6% of patients, 21 times the incidence in the control population (P < 0.001); a retro-aortic left renal vein in 3.2%, four times that in the control population (P < 0.05); and ipsilateral renal agenesis had an incidence of 1% in the test population, 11 times greater than in the control population (P < 0.01). CONCLUSIONS This prospective study of 278 RPLNDs provides evidence that some retroperitoneal anatomical anomalies are associated with testicular germ cell tumours. The link between maldescent and testicular tumours, rather than an isolated association, should be considered as part of a spectrum of retroperitoneal anomalies that occur in these men.