Lesions of naevus of Ota range in colour from light brown to blue, and even greenish-black. To develop guidelines for optimal treatment, we evaluated the number of Q-switched ruby laser treatments required to eliminate the pigmentation of such lesions classified by colour. Over a period of 6 years, we evaluated 151 Japanese patients with naevus of Ota who had been treated with the Q-switched ruby laser at a low energy level (wavelength 694·3 nm; pulse duration 28 × 10−9 s; energy fluence 5 J/cm2; spot size 6·5 mm) every 2 months. Each lesion was classified by colour as brown (n = 22), brown–violet (n = 42), violet–blue (n = 81) and blue–green (n = 6). The 22 predominantly brown lesions attained an excellent (100–95%) or good (95–75%) cosmetic result following three laser treatments in all patients who received this number of treatments. In the 42 brown–violet lesions, 25 of the 29 good or excellent results were achieved after four treatments; the 13 less successful results were in patients who had one to three treatments. In the 81 violet–blue lesions, 54 of the 65 good or excellent results were achieved after four treatments and 64 of 65 after five treatments, whereas all 16 less good results were in patients who had only one to three treatments. However, in the six blue–green lesions, six or more treatments were required to achieve a similarly favourable result. At the end of treatment, the area was virtually free of scarring, and its texture resembled that of the surrounding normal skin. We have confirmed that the use of the Q-switched ruby laser at a low energy level can eliminate the pigmentation of naevus of Ota. While the desired improvement can be obtained within 1 year, the number of treatments appears to depend on the predominant colour of the lesion.