Acute compartment syndrome of the leg has been well documented by numerous authors. To our knowledge, isolated peroneal compartment syndrome has been described in only eight previous cases, all associated with trauma. This case report consists of an isolated peroneal compartment syndrome not associated with any significant trauma. Although the clinical diagnosis was clear and emergency treatment was instituted, magnetic resonance imaging (MRI) was correlated with the clinical and pathological findings. The relevance of this report is that MRI may be useful as a noninvasive tool in exertional muscle disorders in which the clinical diagnosis may not be as clear as it was in this report.