A study was undertaken to investigate the treatment of superficial squamous cell carcinoma of the nasal planum, pinna and eyelid in cats by photodynamic therapy, using topical 5-aminolaevulinic acid cream, with subsequent exposure to red light of wavelength 635 nm, supplied by a light-emitting diode source. A total of 13 squamous cell carcinomas were treated, including 10 nasal planum lesions, two pinnal lesions and one eyelid lesion. After a single treatment, complete responses were seen in nine out of 10 nasal planum lesions, one out of two pinnal lesions and the eyelid lesion. The overall complete response rate for lesions managed with a single photodynamic therapy treatment was 85 per cent. Seven of the 11 lesions (63-6 per cent) showing a complete response subsequently recurred; the time to recurrence ranged from 19 to 56 weeks (median 21 weeks, mean 26-7 weeks).