Insulin deprivation in type 1 diabetes (T1D) individuals increases lipolysis and plasma free fatty acids (FFA) concentration, which can stimulate synthesis of intramyocellular bioactive lipids such as ceramides (Cer) and longchain fatty acid-CoAs (LCFa-CoAs). Ceramide was shown to decrease muscle insulin sensitivity, and at mitochondrial levels it stimulates reactive oxygen species production. Here, we show that insulin deprivation in streptozotocin diabetic C57BL/6 mice increases quadriceps muscle Cer content, which was correlated with a concomitant decrease in the body fat and increased plasma FFA, glycosylated hemoglobin level (%Hb A 1c), and muscular LCFa-CoA content. The alternations were accompanied by an increase in protein expression in LCFa-CoA and Cer synthesis (FATP1/ACSVL5, CerS1, CerS5), a decrease in the expression of genes implicated in muscle insulin sensitivity (GLUT4, GYS1), and inhibition of insulin signaling cascade by Akt␣ and GYS3 phosphorylation under acute insulin stimulation. Both the content and composition of sarcoplasmic fraction sphingolipids were most affected by insulin deprivation, whereas mitochondrial fraction sphingolipids remained stable. The observed effects of insulin deprivation were reversed, except for content and composition of LCFa-CoA, CerS protein expression, GYS1 gene expression, and phosphorylation status of Akt and GYS3 when exogenous insulin was provided by subcutaneous insulin implants. Principal component analysis and Pearson's correlation analysis revealed close relationships between the features of the diabetic phenotype, the content of LCFa-CoAs and Cers containing C18-fatty acids in sarcoplasm, but not in mitochondria. Insulin replacement did not completely rescue the phenotype, especially regarding the content of LCFa-CoA, or proteins implicated in Cer synthesis and muscle insulin sensitivity. These persistent changes might contribute to muscle insulin resistance observed in T1D individuals. type 1 diabetes; skeletal muscle; mitochondria; ceramide; long-chain fatty acid-coenzyme A METICULOUS GLYCEMIC CONTROL in type 1 diabetic (T1D) individuals can be achieved by administration of prandial, shortacting, and long-acting insulin to mimic -cell secretion in response to varying nutrient levels. Metabolic control in these individuals and stringent adherence to guidelines normalize the plasma glucose and glycosylated hemoglobin levels (%Hb A 1c ) and allow for relatively normal life in T1D. Yet T1D individuals are at greater risk of developing cardiovascular disorders and also known to develop insulin resistance (12, 17). The molecular mechanisms responsible for insulin resistance in T1D subjects are unclear, but variable glucose concentrations (28, 70), advanced glycation end products (62, 73), or desensitization of target tissues by insulin (61) have been proposed. Subcutaneous insulin delivery using an insulin pump partially mimics -cell insulin secretion. However, unlike in nondiabetic individuals with twofold higher hepatic insulin concentration than in ...