The relationship between morbidity and physical growth increments was investigated in 716 Guatemalan children ranging in age from 15 days to 7 years. The growth variables investigated were semestral and yearly increments in total body length and weight. The number of days ill with diarrhea, fever, and respiratory illnesses per semester or year was used as an indicator of morbidity. The morbidity data were collected through biweekly retrospective interviews of mothers. Children less ill with diarrhea had substantially larger increments in length and weight than children who were ill with diarrhea a greater percentage of the time. In contrast, fever and respiratory illnesses did not affect growth rates. These findings highlight the fact that diarrhea is a major public health problem in developing nations. © 1975, American Medical Association. All rights reserved.