Introduction Substitute decision making on behalf of incapable patients is based on the ethical principle of ‘respect for autonomy’. This study was conducted to assess patients' wishes and preferences in terms of a substitute decision maker and determinants of such preferences.

Methods The authors conducted a cross-sectional study and selected samples randomly from patients presenting at Farabi Eye Hospital clinics who were 18 years of age or older. Questionnaires were completed through interviews.

Results 200 patients between the ages of 18 and 83 years were interviewed. About 52% (N=105) were men and 73% (N=77) were married. Among married patients, the spouse was chosen as the substitute decision maker in only 51% of cases. Single men preferred their father first in 36% (N=9) of cases, while single girls chose their father in 5.6% (N=1) of cases and their most prevalent choice was other unmentioned people (33.3%, N=6). Most patients (93.5%) wished to be asked about their substitute decision maker when hospitalised.

Conclusion The results of this study show that the people we usually consult for decisions concerning patient treatment are significantly different from the patients' preferred substitute decision makers. The authors suggest patients be allowed to choose their substitute decision maker while conscious.