Background Gallbladder cancer is a rare cancer with a poor prognosis despite all the advances in treatment options and is mostly detected incidentally. In the current literature, re-excision is performed on patients with stage T1b and above, but high mortality rates are still observed. In this study, we aimed to investigate the reasons affecting the prognosis of incidental gallbladder cancer. Methodology Data from 33 patients were retrospectively analyzed. Patient age, sex, preoperative radiologic findings, surgical procedures, margin status, postoperative results with histologic diagnosis, T stage, complications, and mortality were evaluated. Results Of the 33 patients included in the study, 24 (72.7%) were female, nine (27.3%) were male, and the mean age was 66.4 ± 13.4 years. Seventeen (51.5%) patients in our study were aged over 65 years. Age over 65 years was found to have a significant effect on mortality (p = 0.018). In the preoperative ultrasound imaging, 27 (81.8%) patients had gallstones, two (6.1%) patients had gallbladder polyps, 31 (93.9%) had focal or diffuse thickness increases in the gallbladder wall, and nine (27.3%) patients had pericholecystic fluid. The presence of pericholecystic fluid (p = 0.039) and wall thickness (p = 0.006) were found to be associated with mortality. There was perineural invasion and lymphovascular in 17 patients each. Both perineural invasion (p = 0.016) and lymphovascular invasion (p = 0.007) were associated with mortality. Tumor grade was also associated with mortality (p = 0.001). When the prognosis of the patients was evaluated according to the T stage, the increase in the T stage negatively affected the prognosis (p < 0.001). Overall survival was a median of 17 months (95% confidence interval = 10.6-23.3). Conclusions Incidental gallbladder cancer is detected on routine histologic examination of gallbladder specimens after cholecystectomy. Most patients may require re-excision, but the prognosis is still poor in patients who have undergone re-excision. Age >65 years, pericholecystic fluid, T stage, grade, lymphovascular invasion, and perineural invasion had a significant effect on mortality, the presence of which should trigger the option of re-excision to be examined more carefully.