To study the prevalence of mental retardation in Puerto Rico, the proportional distribution of successful retardates, and the processes accounting for success and failure, a random sample of 4,771 adults between the ages of 23 and 49 was screened by the Stanford Binet Form L and a vocabulary test. From this sample, the estimated retardation rate for Puerto Rican adults was 31%. Success was measured by comparing the average income of male retardates with the incomes of other males in the same community; those in the lowest 20% were considered unsuccessful. The proportion of successful retardates was dependent on the complexity of the community; in peasant communities, 78% were successful while in urban non-slums this was reduced to 60%. Intelligence and education contributed to the probability of success, especially for those with IQ's of 85 or above; however, in urban areas retardates with 4 years or less of school had a failure rate of 50% while for those with more schooling the rate was 30%. Over 60% of respondents had a positive self image although normals and successful retardates showed more positive self images (p=.05). Most retardation resulted from cultural deprivation. (MK)