Management of chronic middle ear effusion with prednisone combined with trimethoprim-sulfamethoxazole. Fifty-three patients were enrolled and evaluable in a randomized, double-blinded controlled clinical trial comparing prednisone for 7 days plus trimethoprim-sulfamethoxazole (TMP/SMZ) for 30 days vs. TMP/SMZ alone in treating chronic middle ear effusion (MEE). Clearing of the effusion in both ears or in one when only one was involved was called complete resolution; clearing in one of two affected ears was called partial resolution. The outcomes 2 weeks after initiation of therapy of 26 patients initially treated with prednisone plus TMP/SMZ were complete resolution in 20, partial resolution in three, and unchanged in three. The outcomes in 27 patients initially treated with TMP/SMZ alone were complete resolution in eight, partial resolution in three, unchanged in 13 and development of acute otitis media in three (P less than 0.01 for complete resolution). Two weeks after initiation of therapy, patients with a MEE that failed to clear were crossed over to the alternative regimen. Overall 29 of 41 patients (71%) who received oral prednisone plus TMP/SMZ initially or after the crossover had complete resolution of their middle ear effusion at 2 weeks after starting prednisone and TMP/SMZ. Five of 35 (14%) patients treated with prednisone plus TMP/SMZ and one of six (17%) patients treated with TMP/SMZ alone who had complete resolution at 4 weeks required subsequent referrals for tympanostomy tubes. A course of prednisone for 7 days plus TMP/SMZ for 30 days with monthly follow-up should be considered in children with MEE persisting beyond 6-8 weeks before referral for tympanostomy tube placement. 