Growth and food habits of 399 Age 0 mountain whitefish from the Logan River, Utah, were studied between March, 1970, and April, 1971. At the end of their first six months of life, whitefish were 86-96 mm total length and weighed 6-8 grams (wet). Total temperature experience was 2,950-3,430 degree- days above 32° F. The length-weight relationship for Age 0 mountain whitefish was best described by three stanzas with slopes of 4.3333 for fish 12.5-17.0 mm total length, 3.4437 for fish 17.0-55.0 mm total length, and 2.8043 for fish 50.0-112.0 mm total length. Scalation commenced at 30-35 mm total length and was complete at 40-50 mm total length. Feeding began before yolk-sac absorption was complete and 85 percent of the total diet in numbers was chironomid larvae. Age 0 mountain whitefish in the Logan River fed during daylight and evening hours, and selected chironomid larvae and other food organisms 2-4 mm long.