We report on 498 patients suffering from chronic maxillary sinusitis verified by sinusoscopy through the inferior meatus and by computed tomography of the sinuses, which permitted also the diagnosis of coexisting chronic ethmoidal sinusitis. The patients were treated by temporary drainage through a polyethylene drain tube left in place at the end of the antroscopy for daily lavage with saline solution and daily instillation in the sinus of thiamphenicol glycinate hydrochloride (similar to chloramphenicol) and N-acetyl-l-cysteine. We followed up 847 maxillary sinuses during the lavages according to 2 parameters: 1) recovery of a clean washout product at the macroscopic examination and 2) recovery of normal ostial patency as measured by sinusomanometry. We concluded that 1) the association with ethmoidal sinusitis does not significantly modify the treatment duration, and 2) fewer than 4% of the maxillary sinuses are likely to recover normal parameters after the 23rd day of lavage, and it is therefore useless to continue this treatment much longer. Of the maxillary sinuses, 36.25% were not submitted to any surgery. The results gained by the lavage technique have to be protected from recurrence by the treatment of general, focal, or local causes. © 1993, SAGE Publications. All rights reserved.