There are few published data on plasma cortisol and 17-hydroxyprogesterone (17-OHP) in very-low-birth-weight (VLBW) infants beyond the 1st week of life. We therefore measured plasma cortisol and 17-OHP longitudinally in 26 infants (median birth weight 930 g, median gestational age 28 weeks) from 1 to 16 postnatal weeks to document normative values. We also examined the effect of clinical state on plasma cortisol and 17-OHP levels. Median plasma cortisol decreased with postnatal age from 1 to 8 weeks (110 vs. 60 nmol/l; p = 0.0007) and with postconceptional age from 25 to 36 weeks (104 vs. 47 nmol/l; p = 0.002). Median plasma 17-OHP decreased with postnatal age from 1 to 16 weeks (17.0 vs. 7.1 nmol/l; p < 0.0005) and also with postconceptional age from 25 to 42 weeks (21.1 vs. 7.1 nmol/l; p < 0.0005). Plasma cortisol was not influenced by the clinical state. Median plasma 17-OHP was significantly higher for ‘unwell’ versus ‘well’ infants at 5–8 weeks postnatal age (23.0 vs. 12.5 nmol/l; p = 0.012) but not at other postnatal age intervals. These data provide information on adrenocortical function in VLBW infants during the first 4 months of life.