Trichilemmomas and mucocutaneous papillomatous papules are associated with Cowden syndrome (CS). Germline Phosphatase and tensin homolog (PTEN) mutations have been identified in 34% to 80% of those meeting clinical criteria for CS. PTEN expression has not been well evaluated in large numbers of trichilemmoma. We investigated clinical criteria for CS in trichilemmoma patients and studied PTEN staining to determine how often patients with trichilemmoma have CS and whether PTEN staining is useful. About 102 cases of trichilemmoma or associated lesions from 95 patients were collected. Clinical histories were reviewed to investigate the incidence of CS using International Cowden Consortium operational criteria for diagnosis of CS, version 2000. PTEN staining was performed and graded for intensity and percentage. Although 1 patient had 3 trichilemmoma or associated lesions, and 5 had 2 trichilemmoma or associated lesions, none of 95 patients met clinical criteria for a diagnosis of CS. Twelve of the 89 cases available for staining (13.5%) showed decreased PTEN. Of these, the demographic, clinical, and pathological features were not significantly different compared with PTEN intact cases. None of the cases from the 6 patients with more than 1 trichilemmoma or associated lesions showed decreased PTEN staining. We thus conclude that the likelihood of a clinical diagnosis of CS among patients with a solitary or only a few trichilemmoma is extremely low. PTEN expression is decreased in some sporadic trichilemmomas or associated lesions. This is the largest study investigating clinical history and PTEN staining in patients with trichilemmoma or associated lesions. Because none of our patients met clinical diagnostic criteria for CS, the direct correlation of PTEN in CS and sporadic trichilemmoma remains unclear.