Interventions to avoid atherosclerosis might be more successful if launched early in life when eating and life-style patterns are formed, but dietary interventions have been limited by fears of diet-induced growth failure. We investigated the effects of a diet low in saturated fat and cholesterol on serum lipid concentrations and growth in 1062 healthy 7-month-old infants in a randomised study. Every 1-3 months, families in the intervention group received dietary advice aimed at adequate energy supply, with low fat intake (30-35% energy, polyunsaturated/monounsaturated/saturated fatty acid ratio 1/1/1, and cholesterol intake < 200 mg daily). Infants in control families consumed an unrestricted diet. 3-day food records were collected at ages 8 and 13 months. Growth was carefully monitored. Between 7 and 13 months serum cholesterol and non-high-density-lipoprotein cholesterol concentrations did not change significantly in the intervention group (mean change -0.03 [SD 0.72] mmol/L and 0.01 [0.67] mmol/L) but increased substantially in the control group (0.24 [0.64] mmol/L and 0.23 [0.60] mmol/L; p for difference in mean changes between groups < 0.001). Daily intakes of energy and saturated fat were lower in the intervention than in the control group at 13 months (4065  vs 4370  kJ, p = 0.033, and 9.3 [3.5] vs 14.5 [4.8] g, p < 0.001, respectively), and intake of polyunsaturated fat was higher (5.8 [2.2] vs 4.4 [1.4] g, p < 0.001). Growth did not differ between the groups and was as expected for children at this age. Serum cholesterol concentrations fell significantly in parents of intervention-group infants. The increases in serum cholesterol and non-high-density-lipoprotein cholesterol concentration that occur in infants between the ages of 7 and 13 months can be avoided by individualised diets, with no effect on the children's growth.