A prospective, matched, case-control study conducted over a period of 3 years was designed to examine the association of group A beta-haemolytic streptococcal infections and Henoch-Schonlein purpura. Demographic and clinical data were collected as well as measurement of antistreptolysin O titres and throat swab culture on all children admitted with Henoch-Schonlein purpura, as well as their matched controls. Antistreptolysin O titre positivity was associated with a 10-fold increase in the risk of Henoch-Schonlein purpura. Renal involvement was common among cases with positive antistreptolysin O titres (27%) compared with cases with a negative titre (8%) but this difference has no statistical significance.