After Fisher's introduce of p-value and the cut-off point of 0.05, all clinical studies were evaluated with the statistical significance of the findings. Although the p-value is an objective result but has two important shortfalls. First, although there are significant differences, it has not been found due to insufficient sample size (type II error), and the other is that some statistically significant differences are not clinically important. Minimal clinically important difference (MCID) approach deals with the question of whether the difference is clinically important. MCID concept was described first in 1989 by Jaeschke et al. Although there were statistically significant differences in the use of tools to measure change after treatment, there were no clinically significant differences and they tried to determine the smallest level of clinically significant change. This concept basically includes two elements: 1. the smallest differ-ence that the patient indicates as a change, and 2. the smallest difference that will change the patients treatment approach. In this article, we tried to summarize the MCID approach, describe commonly used methods and briefly explain its application in psychiatry, to evaluate clinical efficacy in the use of patient-reported outcomes. [Anadolu Psikiyatri Derg 2019; 20(3.000): 327-332]