Diaper use is widespread and possibly even increasing across diverse populations in the United States, ranging from infants to very old adults. We found no reports of an experimental analysis of the effect of wearing diapers on the frequency of urinary accidents and the attainment of continence skills (e.g., urinating in the toilet). In this study, we used a withdrawal design to evaluate the effect of wearing diapers on daily urinary accidents and successful voids for an adult who had been diagnosed with mental retardation. Results indicated that wearing diapers increased the rate of accidents and decreased the rate of successful voids. Clinical implications of these results are discussed.