Decision making is a cognitive process that considerably influences nearly every aspect of human life, which shapes outcomes and overall well-being of individuals. This study consisted of two parts, in the first part of which the English version of a 64-item decision-making questionnaire was adapted into Turkish. Responses were collected from 22 pilot and 503 main group participants. The adaptation process involved ensuring language equivalence through translation and back translation, expert reviews and pilot testing to address cultural and linguistic nuances. The validity and reliability of the Turkish version were assessed through a series of statistical analyses. These findings indicated that the adapted questionnaire is a valid and reliable tool for assessing decision-making processes in Turkish-speaking populations. In the second part, the relationship between cognitive flexibility and decision-making abilities was evaluated in a sample of 332 participants. Correlation analysis identified a statistically significant and positive relationship between cognitive flexibility and decision-making (r = 0.233, p < 0.01), indicating that individuals with greater cognitive flexibility tend to perform slightly better in decision-making tasks. The findings underscore the complexity of cognitive and behavioural interactions, emphasising the importance of exploring other mediating and moderating variables in future research.