One hundred and sixteen children with otitis media with effusion underwent myringotomy and insertion of a conventional pattern of Shah grommet in one ear and the much smaller Mini Shah grommet in the other. Close observation post-operatively determined the comparative rate of extrusion, recurrence of effusion, and of onset and degree of tympanosclerosis. At one year review, the Mini Shah shows a significantly earlier extrusion and a greater tendency to recurrence of otitis media with effusion. However, this is compensated by a decreased incidence of tympanosclerosis and reduced severity in those affected. This tends to support the view that shear forces produced by heavier patterns of ventilation tube promote tympanosclerosis.