We report a retrospective case-control study to investigate whether the rotundiform variant of pityriasis versicolor (PV) is significantly associated with the first episodes of PV. Our setting was a dermatology clinic run by a consultant dermatologist. We retrieved medical records of all patients with PV between April 1, 2002 and March 31, 2005. We identified patients with lesions forming closed round circles. We excluded patients with uncertain diagnosis or diagnosis not substantiated by Wood's light examination or skin scrapings for potassium hydroxide examination. For each patient, we retrieved the medical record of the next patient of the same sex and similar age (± three years) with documented non-rotundiform PV and diagnosis substantiated by investigations as the control subject.80 patients were diagnosed as having PV during the record retrieval period. 18 had clinical descriptions or clinical photographs documenting rotundiform PV. Five were excluded owing to uncertain diagnosis, unclear clinical descriptions, or diagnoses unsubstantiated by examination under Wood's light or skin scrapings for potassium hydroxide examination. 13 had definite diagnosis of rotundiform PV. Ten agreed to attend clinic. The response rate was 76.9%. Ten age-and-sex pair-matched control subjects with non-rotundiform PV were recruited. Nine patients with rotundiform PV and two controls with non-rotundiform PV had their episode of PV representing their first episode of PV (p = 0.01; OR = 36.0, 95% CI: 2.2 - 866.9). We conclude that rotundiform PV is significantly associated with the first episode of PV. This phenomenon might be analogous to the herald patch being the primary lesion in pityriasis rosea.