Patients suffering from osteoarthritis (OA) are often tempted to try 'alternative' treatment options. Avocado/soybean unsaponifiables (ASU) have shown some promise for OA. This systematic review is aimed at critically evaluating the data from rigorous clinical trials of ASU. Six databases were searched for randomised, placebo-controlled, double-blind trials of ASU. Four studies could be included. Key data were extracted according to predefined criteria and tabulated as well as discussed in narrative form. The methodological quality of the four studies was high. They included patients with OA of the knee and hip. The dose of ASU was 300 mg/day and one trial also included a group treated with 600 mg/day. Three of the four trials suggested efficacy of ASU for improving the symptoms of OA. The majority of rigorous trial data available to date suggest that ASU is effective for the symptomatic treatment of OA and more research seems warranted. However, the only real long-term trial yielded a largely negative result.