Lactation ketoacidosis is an extremely rare type of high anion gap metabolic acidosis. We report two lactating women who were diagnosed with lactation ketoacidosis. The first patient presented to the Emergency Department at Royal Darwin Hospital, Darwin, Australia, in 2018 with lethargy, nausea and abdominal pain after she commenced a new diet regimen based on three meals of protein per day and free of glucose, gluten and dairy products. The second patient presented to the Emergency Department at Sultan Qaboos University Hospital, Muscat, Oman, in 2018 with headache, severe malaise, epigastric pain and worsening of gastroesophageal symptoms. Blood investigation results showed that both patients had high anion gap metabolic acidosis, ketosis and hypoglycaemia. The patients responded well to intravenous dextrose and resumption of a balanced diet. Both patients were able to continue breastfeeding and remained well on follow-up.