There are provided an endoscopic diagnosis apparatus, lesion portion size detection method, and a non-transitory computer-readable recording medium that enable easy detection of the size of a lesion portion using an endoscope. This object is achieved by capturing an endoscopic image by emitting light having a regular repetitive pattern onto a subject, detecting, from the endoscopic image, a region in which a repetitive pattern is different from the repetitive pattern of the emitted light, and detecting at least one of a length and area of a lesion portion by using a number of repetitive patterns in the region in which the repetitive pattern is different and a size of a unit of repetition in the repetitive pattern.
