Background: The cold/heat questionnaire is one of the most actively developed patient diagnostic tools in traditional Korean medicine (hereafter abbreviated as TKM) because of its objectivity. Unfortunately, the existing questionnaires contain too many items to hold the respondent's attention. In the current study, we aimed to develop an optimized cold/heat questionnaire to be used as a complement to the existing questionnaires. Methods: We developed a new cold/heat questionnaire based on a domain analysis of the existing questionnaires. The questionnaire's reliability was examined via two test–retest reliability analyses involving 1890 individuals in November 2013 and February 2014. Its validity was examined using a professional cold/heat diagnosis kappa value. Results: The new cold/heat questionnaire consisted of a total of seven items, which were created based on an analysis of the existing questionnaires. A reliability analysis performed using the study participants revealed a correlation coefficient of 0.609, 74.5% agreement with professional cold/heat diagnoses by TKM practitioners, and a kappa value of 0.487. Conclusion: In the current study, we developed an optimized cold/heat questionnaire. The level of agreement between the questionnaire and professional cold/heat diagnoses by TKM practitioners was significant, which indicates great potential for its widespread use as a diagnostic tool in TKM.