In a prospective controlled study of the efficacy and sequelae of ventilating tubes, 44 children with bilateral recurrent acute otitis media (greater than 6 episodes/year) and 13 children with bilateral persistent middle ear effusion (greater than 3 months) received unilateral ventilating tube insertion in a randomly selected ear. The contralateral ears were randomized to receive either myringotomy alone or no surgery. Clinical, otoscopic, tympanometric and audiologic examinations were performed before the study and 2 to 4 weeks later, then at 3-month intervals for up to 2 years and at 36 months after surgical randomization. Medical therapy and antibiotic prophylaxis were used whenever indicated. While the ventilating tubes remained functional (mean duration, 10 months) the ears with a tube had significantly fewer episodes of otitis media than their contralateral ear (P less than 0.001; 95% confidence intervals -0.7, -1.7) and had more hearing improvement (P = 0.005; 95% confidence intervals, -5.9, -1.2). After tube extrusion there was a tendency for surgically treated ears to have more otitis and worse hearing, but not at a significant level. Tympanosclerosis, retraction and atrophy were more common in ears that received tubes. The majority of ears treated medically also improved. There is need for a more cautious and selective use of ventilating tubes.