INTRODUCTION: Decompression illness (DCI) results from bubble formation in the blood or tissues following the breathing of compressed gas. Recompression is the universally accepted standard for the treatment of DCI, but a number of strategies have been suggested in order to improve the outcome. METHODS: We performed a systematic search of the literature in December 2007 for randomised controlled trials of DCI therapy, and made an analysis of pre-determined clinical outcomes. RESULTS: Two randomised controlled trials satisfied the inclusion criteria. Pooling of data was not possible. There was a reduction in the number of compressions required with the addition of the non-steroidal anti-inflammatory drug (NSAID) tenoxicam to routine recompression therapy (P = 0.01) but no evidence of improved effectiveness (relative risk (RR) of residual symptoms 1.04, P = 0.58). The risk of multiple recompressions was lower with heliox than with an oxygen treatment table (RR 0.56, 95% CI 0.31 to 1.00, P = 0.05). CONCLUSIONS: There is no randomised evidence concerning the effectiveness of recompression for DCI. Either the addition of an NSAID or the use of heliox may reduce the number of recompressions required, but neither strategy is shown to improve the chance of recovery. The application of either of these strategies may be justified. The modest number of patients studied demands a cautious interpretation of the findings. There is a case for large randomised trials of high methodological rigour in order to define any benefit from the use of different breathing gases during recompression therapy.