Background  Xeroderma pigmentosum type C (XP-C) is a rare, autosomal, recessive condition characterized by the association of various clinical manifestations mostly involving the skin and eyes.

Objectives  To evaluate the clinical manifestations in a homogeneous, genetically characterized cohort of patients with XP-C.

Methods  All patients with XP-C, which was confirmed genetically or by unscheduled DNA synthesis, from the registry of our department and from the French association of patients ‘Les Enfants de la Lune’ were contacted. During a planned consultation, clinical information was collected using a standardized case-record form.

Results  In total, 31 patients were seen. The mean age at diagnosis was 2·95 years; skin symptoms started at a mean age of 1·49 years. Among the patients, 52% had relatively short stature, with a height-for-weight z-score below −1 SD; 62% showed pyramidal syndrome and 45% had photophobia and/or conjunctivitis. Four patients had several pyogenic granulomas. Twenty-four patients (77%) had skin cancer. The mean age of onset of the first skin cancer was 4·76 years (range 2–14·5 years). Basal-cell carcinoma was the most frequent cancer. Melanomas were rare and mostly desmoplastic. Multinodular thyroid was the most frequent internal tumour.

Conclusions  Our data highlight several new aspects of XP-C. Patients with XP-C are at risk of developing pyogenic granulomas, desmoplastic melanomas and multinodular thyroid. Involvement of the central nervous system is frequent, but its mechanism remains unclear. The relatively short stature of the patients needs further investigation in order to be explained. XP-C is not only a cancer-prone disorder but is also a polysystemic disorder.