The diagnosis chylothorax is based on a chemical analysis of the pleural effusion. According to the literature, this analysis can be rather straightforward, comprising measurements of triglycerides, chylomicrons, and cholesterol. In this report we present an autopsy case that alerted us to interpret these results critically. Although the laboratory tests of the pleural effusion in this patient with parenteral nutrition suggested chylothorax, additional tests (potassium (11.3 mmol.L(-1)) and glucose (128 mmol.L(-1)) proved otherwise. Comparison of the pleural effusion analysis and the content of the parenteral nutrition led to the final conclusion that the effusion was due to a leakage of parenteral nutrition instead of chylothorax. We therefore suggest adding glucose and potassium measurements to the biochemical work-up of a patient under suspicion of chylothorax.