1148 patients underwent retinal detachment (RD) surgery between october 1st 1969 and december 31st 1979 with follow up assured until june 30th 1983 non idiopathic retinal detachments were excluded from this study which was focused on the risk factors concerning detachment of the second eye. With this time criteria the present rate of RD on the second eye is 4,03% : 39 eyes in 970 patients for whom the second eye was present examinable and free of any RD at the time of the first examination. A statistical analysis with the X2 test shows that male patients (p less than 0,025) and heavily myopic eyes (p less than 0,025) are at greater risk; giant tears (70 degrees and more) in the first eye are also an important risk factor. When it comes to preexisting peripheral lesions, the data are more confusing. While the absence of such lesions is not protective against detachment, the contralateral eyes of patients with so-called dangerous lesions may remain detachment-free for a very long time without any treatment. We think that the best prophylactic treatment consists of an equatorial 360 degrees argon laser photocoagulation, with the following indications: giant tear, any break, and peripheral degenerations that lead to a progressive thinning of the inner retina. Care must be taken not to perform heavy photocoagulation therapy on eyes harboring a cellular, densified vitreous.