Calcific uremic arteriolopathy, formerly known as calciphylaxis is a devastating condition that primarily affects patients with end-stage renal disease. The lesions can progress to massive ulcerations of the subcutaneous tissue that are associated with a high degree of morbidity and mortality, usually related to sepsis. Although the pathophysiology of this condition is poorly understood, it appears to be related to a derangement in calcium–phosphate metabolism. Thus, treatments have focused on the treatment of hyperparathyroidism albeit with poor results. More recently, sodium thiosulfate (STS) has emerged as a promising therapy following multiple case reports of marked disease regression following its use. As STS is a strong acid, metabolic acidosis has been described following its administration, although relatively mild in degree. We report a case of a patient with calciphylaxis who repeatedly developed a severe anion gap metabolic acidosis following each dose of STS requiring a significant reduction in the dose.