Plasma fatty acid patterns were analysed in 15 children aged 2 to 42 months (median = 12 months) admitted to the University Hospital, Faculty of Medicine of Ribeirão Preto, University of São Paulo, suffering from grade III protein-energy malnutrition in its different clinical forms: marasmus (n = 5), marasmic kwashiorkor (n = 5), and kwashiorkor (n = 5). A control group of eight children from the same population aged 3 to 22 months (median = 12 months) was also studied. Plasma fatty acids were analysed by gas liquid chromatography. The plasma fatty acid patterns detected in grade III protein-energy malnutrition indicated changes characteristic of essential fatty acid deficiency, with lower linoleic acid (C18:2) levels in the three groups (p < 0.05). The major metabolite of linoleic acid, arachidonic acid (C20:4), was lower in the kwashiorkor group than in the control group (p < 0.05). Linoleic acid (C18:2) levels were lower in the marasmus group than in the kwashiorkor group (p < 0.05). Several factors may have contributed to these changes, such as a decreased content of linoleic acid in the diet, plus malabsorption and/or poor utilization of fats, and changes in the synthesis or degradation of these fatty acids. Although many questions remain unanswered, we suggest that an adequate amount of linoleic acid be added to the rehabilitation diet of these children in the form of vegetable fat.