Nine hundred babies born at Ankara Maternity Hospital were studied for neonatal diaper dermatitis during the first four days of life. None was seen on the first day, but on the second day the incidence was 1.8 per cent, on the third day, 2.5 per cent, and on the fourth day, 2.0 per cent. All the babies were breast-fed, and stool and urine pH values of 40 babies, tested over the four day period, were consistently acid. The author concludes that feeding is an important etiological factor in neonatal diaper dermatitis because of its effect on feces pH.