For the epidemiological surveys and evaluations of therapy, it is essential to evaluate the severity of diseases. There are several reported methods of assessment for acne severity including lesion counting, comparison of the patient's to a photographic standard and comparison of the patient's to a text description. But all of these are based on opinions of specialists. In this study, we attempted to make an evidence-based grading criteria for acne severity, which was expected to yield consents from most dermatologists. The dermatologists consulted classified the global severity of acne patients without any standard and then counted the numbers of eruptions. Three independent expert dermatologists graded the photographs of these patients. We compared the verdicts of the consulted dermatologist and three experienced dermatologists, and analyzed the relationships between these classifications and numbers of eruptions. Our results showed that most of the dermatologists have similar latent recognitions of acne severity. We selected representative photographs as standards, which would contribute to making adjustments for judgments. Global classifications of dermatologists correlated with numbers of inflammatory eruptions (papules plus pustules), but did not with numbers of comedones. The appropriate divisions of inflammatory eruptions of half of the face to decide classifications were: 0-5, "mild"; 6-20, "moderate"; 21-50, "severe"; and more than 50, "very severe".