Palmoplantar keratoderma-XX sex reversal-predisposition to squamous cell carcinoma syndrome is characterized by sex reversal in males with a 46, XX (SRY-negative) karyotype, palmoplantar hyperkeratosis and a predisposition to squamous cell carcinoma. To date, five cases (four of whom were brothers) have been described. The etiology is unknown. The disease is palmoplantar keratoderma-XX sex reversal-predisposition to squamous cell carcinoma syndrome (Monarch Disease Ontology entry MONDO_0012530). Also known as: palmoplantar hyperkeratosis with squamous cell carcinoma of skin and sex reversal, palmoplantar hyperkeratosis-XX sex reversal-predisposition to squamous cell carcinoma syndrome.