Antimalarial medications carry a risk of rare, but serious side effects. Primaquine in particular is known to cause methemoglobinemia and hemolytic anemia. In patients with underlying glucose-6-phosphate dehydrogenase (G6PD) deficiency, these side effects become amplified and can be life-threatening. This can complicate treatment plans as the recommended first-line management of severe methemoglobinemia, methylene blue, may cause or worsen hemolytic anemia in G6PD deficient patients. We present a case of a toddler with an accidental primaquine overdose who had undiagnosed G6PD deficiency. Over the 2 days following his ingestion he developed severe methemoglobinemia and hemolytic anemia toxicity. He was initially treated with a dose of methylene blue prior to learning of his G6PD deficiency. He was subsequently given additional doses of ascorbic acid and a blood transfusion. His condition gradually improved and he was ultimately discharged in good condition. To our knowledge, this case represents a unique presentation of mixed methemoglobinemia and hemolytic toxicity due to an accidental primaquine overdose in a G6PD deficient pediatric patient. Though cases remain relatively rare, pediatric patients represent the vast majority of known primaquine overdoses. Their diagnosis and treatment require maintaining a high index of suspicion and a good working knowledge of antimalarial toxicities and management options.