Eighty-three infants with classical phenylketonuria have been born in Norwa
y since 1979. The treatment of these children is centralized at the Nationa
l Hospital in Oslo. Seventy-four have been breastfed in combination with a
phenylalanine-free protein substitute. Dietary treatment was commenced in h
ospital between 5 and 33 d of age (mean 14 d). Normalization of serum pheny
lalanine (below 400 mu mol/l) took between 1 and 35 d (mean 8 d). The perio
d of breastfeeding lasted from 1 to 16 mo (mean 7 mo). Growth (weight, leng
th and head circumference) fell within the normal range for age on the Norw
egian growth chart.