BACKGROUND: Lactic acidosis (LA) is a complication of diseases commonly seen in intensive care patients which carries an increased risk of mortality. It is classified by its pathophysiology; Type A results from tissue hypo-perfusion and hypoxia, and Type B results from abnormal metabolic activity in the absence of hypoxia. Reports of the co-occurrence of both types have been rarely reported in the literature relating to intensive care patients. This case report describes the challenging management of a patient diagnosed with both Type A and Type B LA. CASE PRESENTATION: A 55-year-old female with newly diagnosed diffuse large B-cell lymphoma (DLBCL) developed hospital-acquired pneumonia, respiratory failure, shock and intra-abdominal septicaemia from a bowel perforation. Blood gases revealed a mixed picture lactic acidosis. Correction of septic shock, respiratory failure and surgical repair caused initial improvement to the lactic acidosis, but this gradually worsened in the intensive care unit. Only upon starting chemotherapy and renal replacement therapy was full resolution of the lactic acidosis achieved. The patient was discharged but succumbed to her DLBCL several months later. CONCLUSION: Type A and Type B LA can co-occur, making management difficult. A systematic approach can help diagnose any underlying pathology and aid in early management.