Characteristics of rhegmatogenous retinal detachment and its predisposing factors were studied in a consecutive series of 342 patients operated on for retinal detachment (RD) at the University Eye Hospital in Helsinki in 1978-1981. On these, 234 were pre-operatively examined and operated on by the senior author. The mean age of the patients was 52.8 +/- 1.0 (range 5.7 to 83.0) years, 49.1% were males, 50.9% females. Bilateral RD occurred in 9.9%, and another 4.7% had been treated for retinal breaks in the fellow eye. Of the main predisposing factors, myopia (greater than or equal to -1.0 D) was found in 50.6% of the phakic eyes, 23.0% of the eyes were aphakic, and lattice degeneration was found in 15.1% and trauma in 11.9% of the whole series. In the nontraumatic phakic group, lattice degeneration was present in 31.3%. In the aphakic group, 25.9% had underlying myopia and 8.1% showed lattice degeneration. The relative importance of these factors varied with age. Total RD was found in 60 eyes (17.0%), most commonly in aphakic eyes (32.1%). Macula was detached in 56.5%. Two or more retinal breaks were found in 40.9%. The type of breaks varied with age and refraction. Oral dialysis was common before the age of 20 in non-myopic phakic eyes. Between 20 and 39 years, tears and holes were equally common, and after 40 years of age tears predominated. Tears outnumbered holes both in nonmyopic and myopic eyes, most round holes were found in myopic eyes. In 11.6% of the eyes no sure retinal breaks were detected. Relation of retinal breaks to peripheral retinal degenerations was studied.