Apart from clinical observations of Ménière's disease in children, there have only been a few histological descriptions of endolymphatic hydrops (EH) as an incidental finding in children. In this paper we report on the incidence of EH in temporal bones of children. One hundred eighteen temporal bones from 70 infants between newborn and 10 years (average age 12.9 months) were analyzed by light microscopy for EH of the cochlear duct, which was defined as a bulging of Reissner's membrane into the scala vestibuli in more than one turn of the cochlea. All endolymph spaces were carefully examined for factors such as an obliterated ductus reuniens which may have contributed to the development of EH. In 64 (54.2%) of the 118 temporal bones, a bulging of Reissner's membrane in the cochlear duct was found. In 65.6%, the bulging was confined to the apical turn and since the significance of isolated apical hydrops is controversial, we elected not to consider this group as having hydrops. Twenty (16.9%) bones met our criteria for a diagnosis of EH. Compared to the high incidence of bulging in the cochlear duct, fewer saccules and utricles were dilated. In approximately half of the temporal bones (49.2%), the ductus reuniens was collapsed. The ductus reuniens seems to be closed in its normal position and might open when pressure occurs due to an increasing volume of endolymph. If there is a permanent closure, EH may result. Our investigation does not indicate that EH is associated with a specific disease; however, where there were congenital anomalies the incidence of EH was higher.(ABSTRACT TRUNCATED AT 250 WORDS)