Carpal tunnel syndrome, though generally successfully treated by surgical decompression, still results in significant morbidity. The causes remain unclear and there is uncertainty about appropriate investigations for diagnosis and assessment of severity. The best nonsurgical treatment is yet to be fully elucidated. Recent work has begun to cast some light on these uncertainties.The pathology of idiopathic carpal tunnel syndrome is a noninflammatory fibrosis of the subsynovial connective tissue surrounding the flexor tendons. Biochemical studies of surgical specimens suggest that a variety of regulatory molecules may be inducing fibrous and vascular proliferation and that this may be a response to mechanical stresses. Ultrasound imaging has begun to demonstrate its ability to accurately image the carpal canal contents and the diagnostic value of measurements of median nerve cross-sectional area showing expansion of the nerve is becoming established. The sensitivity and specificity of such measurements may be comparable to those of nerve conduction studies, though their prognostic value remains unknown. Nonsurgical treatment with steroid injection may be a more effective treatment than previously recognized, and is under used.Suspected carpal tunnel syndrome should be investigated first with nerve conduction studies but consideration should be given to the use of magnetic resonance imaging or ultrasound imaging when diagnostic uncertainty remains, or there is a suspicion of a space occupying lesion in the carpal canal, especially if endoscopic surgery is contemplated. Treatment by local steroid injection should be considered a valid alternative treatment, at least for milder cases.