Background Significant variability exists for the relative risk (RR) of testicular malignancy in isolated cryptorchidism.

Objective To perform a meta-analysis to clarify the true magnitude of this risk, allowing clinicians to better counsel patients and their families.

Setting Secondary research conducted by undergraduate researchers, clinical academics and a clinical statistician.

Design, data sources, and methods A search of the English literature was performed for studies relating to testicular cancer and cryptorchidism, published between 1 January 1980 and 31 December 2010, using Embase and Medline databases. 735 papers were identified and analysed by four authors independently in accordance with our inclusion and exclusion criteria. Studies reporting an association between cryptorchidism and subsequent development of testicular malignancy were included. Genetic syndromes or other conditions which predisposed to the development of cryptorchidism were excluded. Pooled estimates and 95% CIs for the RRs were calculated.

Results Nine case–control studies and three cohort studies were selected. The case–control studies included 2281 cases and 4811 controls. Cohort studies included 2 177 941 boys, with a total of 345 boys developing testicular cancer (total length of follow-up was 58 270 679 person-years). The pooled RR was 2.90 (95% CI 2.21 to 3.82) with significant heterogeneity (p<0.00001; I²=89%).

Conclusion Boys with isolated cryptorchidism are three times more likely to develop testicular cancer. The limitations of this study must be acknowledged, in particular, possible publication bias and the lack of high-quality evidence focusing on the risk of malignancy in boys with isolated cryptorchidism.