The incidence of medicolegal claims based on retinopathy of prematurity (ROP) diminished in the 1960s after the role of oxygen was presumed to be understood. It has since increased again for a number of reasons. More very premature infants are being saved. The causes of ROP are multifactorial, not well understood, and the role of oxygen as a significant factor is not always clear. Moreover, the risk/benefit ratio of supplemental oxygen is not always easy to evaluate. The morphologic features of ROP are common to a number of disorders, which may be misdiagnosed as ROP. In the series of 500 medicolegal claims that I have studied, no ophthalmologists have been sued in cases concerning ROP. However, they are routinely called as expert witnesses and it is to guide them in that role that I am reviewing the subject.