300 patients with pityriasis versicolor, 168 males and 132 females, of different ages were included in this study. Each was subjected to a detailed structured questionnaire. All the available relatives had been examined. Pedigrees were constructed and segregation analysis was done using the mathematics of population genetics. The collected data showed genetic susceptibility which is inconsistent with any of the single gene defects but fulfill the criteria of multifactorial (genetic-environmental) inheritance. The heritability was estimated to be 22.2% in the first-degree relatives.