AIM: The Ethiopian primary care of sick children is provided within the integrated Community Case Management of childhood illnesses by Health Extension Workers (HEW). There is limited knowledge whether this cadre correctly assess and classify common diseases. The aim was to study their ability to correctly classify common childhood illnesses. METHODS: A survey was conducted from December 2016 to February 2017 in four regions of Ethiopia. Observations of the HEWs' assessment and classification of sick children were followed by child re-examination by a trained health officer. RESULTS: The classification by the HEWs of 620 sick children as compared to the re-examiner had a sensitivity of 89% and specificity of 94% for diarrhoea, sensitivity 52% and specificity 91% for febrile disorders, and a sensitivity of 59% and specificity of 94% for acute respiratory tract infection. Malnutrition and ear infection had a sensitivity of 39 and 61%, and a specificity of 99 and 99%, respectively. CONCLUSION: Most cases of diarrhoea were correctly classified, while other illnesses were not frequently identified. The identification of malnutrition was especially at fault. These findings suggest that a significant number of sick children were undiagnosed that could lead to absent or incorrect management and treatment.