The article discusses diagnostic difficulties in patients with acute abdominal pain. The author adduces data on the frequency of late diagnostics of pleuropneumonia and diaphragmatic pleuritis in patients with abdominal syndrome before admission, and in the admission department of an urgent aid hospital. The analysis of the causes of delayed diagnosis of lung and pleura diseases is exemplified with 2 clinical observations. The article also covers ways of prevention of diagnostic errors in patients with abdominal pain.