Authors present the case of a 37-year-old man admitted to the emergency room of Universidade Federal de São Paulo-Escola Paulista de Medicina, with hyperosmolar coma, following progressive muscle discomfort and loss of renal function, with further need of dialysis therapy. Initial laboratory evaluation showed marked hyperglycemia, hypernatremia, hyperosmolarity, and high levels of creatinine. In the evolution he presented an elevation of creatino-phosphokinase levels in parallel with increasing levels of urea and creatinine. Urinalyses showed progressive increase in proteinuria and hematuria. A muscle biopsy was performed and confirmed the presence of muscular necrosis. The purpose of this paper is to emphasize hyperosmolarity as a newly described cause of rhabdomyolysis. The authors point out its multifactorial physiopathology and also stress the relatively common occurrence of acute renal failure (ARF) following an episode of rhabdomyolysis, and the poor prognosis that this complication represents.