Summary Using data from a longitudinal study conducted in 40 villages by the UK MRC in the North Bank Division of The Gambia beginning in late 1981, we examined infant and child mortality over a 15‐year period for a population of about 17 000 people. Comparisons are drawn between villages with and without PHC. The extra facilities in the PHC villages include: a paid Community Health Nurse for about every 5 villages, a Village Health Worker and a trained Traditional Birth Attendant. Maternal and child health services with a vaccination programme are accessible to residents in both PHC and non‐PHC villages. The data indicate that there has been a marked improvement in infant and under‐five mortality in both sets of villages. Following the establishment of the PHC system in 1983, infant mortality dropped from 134/1000 in 1982–83 to 69/1000 in 1992–94 in the PHC villages and from 155/1000 to 91/1000 in the non‐PHC villages over the same period. Between 1982 and 83 and 1992–94, the death rates for children aged 1–4 fell from 42/1000 to 28/1000 in the PHC villages and from 45/1000 to 38/1000 in the non‐PHC villages. Since 1994, when supervision of the PHC system has weakened, infant mortality rates in the PHC villages have risen to 89/1000 in 1994–96. The rates in the non‐PHC villages fell to 78/1000 for this period. The under‐five mortality rates in both sets of villages have converged to 34/1000 for 1994–96. When the PHC programme was well supported in the 1980s, we saw significantly lower mortality rates for the 1–4‐year‐olds. These differences disappeared when support for PHC was reduced after 1994. The differential effects on infant mortality are less clear cut.