Ultrasound therapy is used frequently to reduce pain and related disability, mainly by physiotherapists. The objective of this review was to evaluate the effectiveness of ultrasound therapy in the treatment of musculoskeletal disorders. Published reports of randomized clinical trials investigating the effects of ultrasound therapy on pain, disability or range of motion were identified by a systematic search of MEDLINE, EMBASE and the Cochrane databases, supplemented with citation tracking. The quality of methods of all selected publications was assessed systematically by two independent and 'blinded' reviewers, using ten validity criteria. Data from the original publications were used to calculate the differences between groups for success rate, pain, disability and range of motion. Statistical pooling was performed if studies were homogeneous with respect to study populations, interventions, outcome measures and timing of follow-up. 38 Studies were included in the review, evaluating the effects of ultrasound therapy for lateral epicondylitis (n = 6), shoulder pain (n = 7), degenerative rheumatic disorders (n = 10), ankle distorsions (n = 4), temporomandibular pain or myofacial pain (n = 4) and a variety of other disorders (n = 7). In 11 out of 13 placebo-controlled trials with validity scores of at least five out of ten points, no evidence of clinically important or statistically significant results was found. Statistical pooling was only feasible for placebo-controlled trials on lateral epicondylitis, and produced a pooled estimate for the difference in success rate of 15% (95% confidence interval -8%-38%). As yet, there seems to be little evidence to support the use of ultrasound therapy in the treatment of musculoskeletal disorders. The large majority of 13 randomized placebo-controlled trials with adequate methods did not support the existence of clinically important or statistically significant differences in favour of ultrasound therapy. Nevertheless, our findings for lateral epicondylitis may warrant further investigation.