Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) is an autosomal recessive mitochondrial fatty acid beta-oxidation disorder with variable presentation including lack of energy (lethargy), low blood sugar (hypoglycemia), weak muscle tone (hypotonia), hepatic steatosis, and hypocarnitinemia. In this report, we describe a 9-month-old male patient who suffered from recurrent hypoglycemia with hypoglycemic convulsions, vomiting, and neurological regression since the age of 4 months. The patient presented with hypotonia, motor delay, hepatomegaly, protein-energy malnutrition (BMI SDS — 2.8). Biochemical tests demonstrated hypoglycemia (2.5 mmol/l), elevated lactate, creatine phosphokinase, and aminotransferases. There were also increased concentrations of long-chain acylcarnitine and 3-hydroxyacylcarnitine as well as a dramatic decrease in the carnitine level. Digestive tract malformations, endocrinopathies, and degenerative diseases of the nervous system were excluded hydroxyacyl-CoA dehydrogenase (HADHA) gene) testing revealed a homozygous mutation p.Glu474Gln. This confirmed the diagnosis of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency. Diet correction by adding medium chain triglycerides, compensation of carnitine deficiency, and symptomatic therapy made it possible to avoid fatal metabolic crises and manage neurological regression. Early detection, diagnosis, and treatment of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency may improve clinical outcomes.