Trigger thumb is a flexion deformity of the thumb interphalangeal joint due to constriction of flexor tendon sheath which interferes with normal smooth gliding of the tendon within in tendon sheath. Characteristically there is a palpable nodule on the tendon at the level of metacarpal head associated with thickening of fibrous tendon sheath. The etiology is thought to be congenital, traumatic or combination of both. But it is hard to visualize that trauma is the sole etiologic factor in infant or children who are not subject to repetition of trauma as in adults. The 35 thumbs of 30 children and infants treated at Kyungpook National University Hospital from June, 1983 to August, 1989 were reviewed, with special reference to pathologic findings. The results were as follows;1. In the 30 patients, a total of 35 thumbs were affected. 2. Male were 12 cases, and female, 18 cases. Right thumb were 12 cases, left thumb, 13 cases and both thumbs, 5 cases. 3. The age first noticed by parents varies from birth to 11 years old. Mean of age is 2.5 years old. 4. Physical examination revealed a flexion deformity of the thumb interphalangeal joint below 10 degrees in 8 cases, 10-20 degrees in 5 cases and 20-30 degrees in 2 cases. The palpable node (Notta's node) was felt at the level of metacarpophalangeal joint in all cases. Snapping was felt in 20 cases. 5. A1 pulley resection was done in all cases. 6. Variable findngs were observed in the tendon and its sheath at the operative field. Of these, diffuse bulbous thickening of tendon was 24 cases(68.6%), A1 pulley was broadened(16 cases) or thickened and sclerotic (17 cases). 7. Light microscopic findings of tendon and synovium were obtained in 9 cases. Non-inflammatory fibrosis were 8 cases, and no pathologic changes, 1 cases. No cases had chronic inflammatory change. 8. Corresponding to light microscopic findings of synovium, inflammatory changes were not seen in scanning electron microscopy. 9. The operative treatment was satisfactory. Of surgically treated 35 thumbs, 33 thumbs (94.3%) were corrected. Unsatisfactory cases were persistence (1 case) and recurrence (1 case).