Background To examine the risk factors for an early postoperative intraocular pressure (IOP) increase after ab interno trabeculotomy using a Kahook Dual Blade (KDB trabeculotomy). Methods A retrospective study was performed in 76 exfoliation glaucoma (EXG) eyes and 56 primary open angle glaucoma (POAG) eyes that underwent KDB trabeculotomy, with or without cataract surgery at Kumamoto University Hospital. Postoperative high IOP was classified as IOP≥20 mmHg (within three months after surgery, whether persistent or temporary), transient IOP≥20 mmHg (IOP≥20 mmHg after surgery, then dropped below 20 mmHg), and the presence of IOP spikes (≥ 10 mmHg from baseline). Risk factors were examined using logistic regression analysis. Results The preoperative mean IOP (SD) was 24.98 (7.23) mmHg in patients with EXG and 21.28 (6.58) mmHg in patients with POAG. IOP was reduced by 32.1% in patients with EXG and by 17.7% in patients with POAG at 6 months after surgery. Postoperative IOP≥20 mmHg was observed in 56.6% of EXG patients and in 51.8% of POAG patients. IOP spikes occurred in 15.8% of EXG patients and in 14.3% of POAG patients. Logistic regression analysis showed that factors with significant odds ratios (ORs) were age (OR = 0.866, 95% CI = 0.793–0.945), preoperative medication use (OR = 2.02, 95% CI = 1.17–3.49), trabeculotomy in combination with cataract surgery (OR = 0.0674, 95% CI = 0.015–0.303), and IOP at day 1 (OR = 1.41, 95% CI = 1.18–1.68) for postoperative IOP≥20 mmHg, the IOP at day 1 (OR = 1.1, 95% CI = 1.03–1.17) for transient IOP≥20 mmHg, and age (OR = 0.948, 95% CI = 0.901–0.997) and preoperative IOP (OR = 0.83, 95% CI = 0.736–0.936) for IOP spikes. Conclusion Although KDB trabeculotomy is an effective treatment for patients with EXG and POAG, patients who take multiple preoperative medications and have a high IOP on day 1 require careful follow-up to prevent postoperative IOP elevation.