The therapeutic effect of ultrasonographically guided aspiration of a ganglion cyst of the shoulder is evaluated. Fifteen patients (nine male, six female) with chronic shoulder pain were enrolled in this study. Each patient was referred to rule out rotator cuff lesion. The ultrasonographic examination showed an anechoic cystic lesion in the shoulder region in every patient and abnormality of the rotator cuff in only four patients. Under ultrasonographic guidance, an 18 gauge needle was inserted into the cyst to aspirate the fluid. Initial sonographic imaging showed the cyst, which appeared as a localized fluid accumulation and was located between the deltoid muscle and the subscapularis tendon in seven patients, between the deltoid muscle and the biceps tendon in one patient, below the coracoacromial ligament in five patients, and over suprascapular notch area in one patient. The ganglion cysts ranged in size from 3.5 to 30 mm. The amount of aspirated fluid in each cyst varied from 0.4 to 12 ml (mean, 2.6 ml +/- 3.1) with a clear or light yellowish color and a jelly-like appearance. No major complications occurred during or after this procedure. The symptom (pain) was improved after sonographically guided aspiration in each patient. Follow-up study showed complete relief of pain in four patients, marked improvement in nine patients, and mild improvement but still persistent shoulder pain in two patients. Duration of follow-up study ranged from 2 to 24 months (mean, 6.4 months +/- 6.9). The success rate for sonographically guided aspiration was 86% on the basis of marked symptom improvement or relief. Ultrasonographically guided aspiration of shoulder ganglion cysts is an effective procedure in the management of shoulder pain caused by ganglion cysts.