Fecal fat microscopy using the Sudan stain has suffered from a relative lack of specificity, and results are "qualitative." Therefore, we developed a quantitative fecal fat microscopic method with hopes of improving diagnostic accuracy. One hundred eighty patients with chronic diarrhea collected stools for 1 to 3 days, and fecal fat output was measured by a standard chemical method, and microscopy was performed by the old qualitative and new quantitative methods. There was a highly statistically significant linear correlation between quantitative fecal fat microscopy and chemically measured fecal fat output. The quantitative microscopic method had a sensitivity of 94% and a specificity of 95%; the traditional method had a sensitivity and specificity of 76% and 99%, respectively. Fecal fat Sudan microscopy performed by a dedicated approach to counting and size measurement of fat globules can yield a quantitative result that correlates well with chemically measured fecal fat output and has a high diagnostic accuracy.