Purpose: To evaluate the incidence of intraocular pressure (IOP) spikes within the first postoperative hours following trabeculectomy (TRAB) and to determine possible associated factors. Methods: An observational study was carried out. We enrolled consecutive patients undergoing standard TRAB with mitomycin C. They were examined twice within the first few postoperative hours (hours 1-2 and 4-6) and 3 times after TRAB (on days 1, 7, and 30). Demographic and ocular data were collected. Main outcome measurements were postoperative IOP values at each time point and the frequency of IOP spikes, defined as IOP ≥25 mm Hg. Results: A total of 40 eyes of 40 patients were included (mean age 59.62 ± 13.37 years). Although IOP was significantly reduced to 11.14 ± 7.99 mm Hg at hours 1-2 (p < 0.01) and to 11.52 ± 7.30 mm Hg at hours 4-6 (p < 0.01), IOP spikes were documented in 3 patients (7.5%). In the group of patients with IOP spikes, we noted that there was a high incidence of black patients and that the surgeries had been performed by fellow surgeons. Conclusion: Although the majority of the cases (92.5% of the patients) did not present IOP spikes, 7.5% of our patients presented the event. In selected cases, such as those with advanced disease, fixation threat, and of black race, IOP should be monitored during the first few postoperative hours for the identification and adequate management of potential IOP spikes, preventing undesirable outcomes.