The study investigated the influence of gender and psychological factors on subjective well-being (SWB) in 191 adults with functional dyspepsia (FD) after their first upper gastrointestinal endoscopy. Participants were divided into two subgroups: a larger group of highly educated working-age individuals and a smaller group of older adults over 60 with higher rates of comorbidity. The strongest predictors of SWB were psychological factors—stress resistance and somatization, while health and lifestyle factors had moderate effects. Gender emerged as a significant determinant of SWB only after controlling for somatization and stress resilience. Path analysis revealed complex causal pathways between gender, psychological variables, and SWB, including other gender-related factors. The results support the biopsychosocial model of FD and highlight the need to include somatization and stress resilience in SWB studies, with separate assessments of younger and older individuals.