We present a 12-year-old boy who developed subacute thyroiditis during the course of rapidly progressive glomerulonephritis due to Henoch-Schonlein purpura (HSP) proven by clinical findings and percutaneous renal needle biopsy. The thyroid gland of the patient suddenly enlarged with mild tenderness while he was on steroid and dipyridamole therapy. Thyroid hormone levels revealed T3 0.31 ng/ml (nl: 0.52-1.75 ng ml), T4 2.53 ug/dl (nl: 4.8-12.8 ug/dl), free T3 0.80 pg/ml (nl: 2.14-5.34 pg/ml), free T4 0.2 ng/dl (nl: 0.73-1.95 ng/dl) and TSH 1.02 U/ml (nl: 0.36-3.25 U/ml). Antimicrosomal antibody was negative while antithyroglobulin antibody was slightly positive (1/80+). Hypoactivity with a spotty pattern was demonstrated by thyroid scanning. Serologically proven mumps infection was detected and may have been a triggering factor in the development of both HSP and subacute thyroiditis.