Background/Objectives: Oral hygiene is an essential component of overall health, but is often neglected during hospital stays, particularly among patients who rely on healthcare providers for daily care. Poor oral hygiene may lead to discomfort, infections, and complications such as hospital-acquired pneumonia. The objective of this study was to assess the oral hygiene practices of hospitalized patients in Al-Ahsa, Saudi Arabia. Methods: A hospital-based cross-sectional study was conducted among patients in public and private hospitals. Since no prior studies existed for this population, a pilot study with 60 participants was used to estimate the population proportion for sample size calculation. Based on the pilot findings, a proportion of 80% was assumed, with a 95% confidence level, 5% margin of error, and 80% power. Patients were recruited through non-probability convenience sampling. Data were collected via structured face-to-face interviews and analyzed using SPSS version 27. Descriptive statistics, chi-square tests, and logistic regression were applied, with significance set at 0.05. Results: Regular toothbrushing declined from 69.6% before admission to 29.8% during hospitalization. Only 29.8% of patients received oral hygiene supplies, and 79.2% received no assistance. In-hospital toothbrushing was significantly associated with being female (AOR = 2.52; 95% CI: 1.17–5.43), non-Saudi (AOR = 3.91; 95% CI: 1.22–12.55), and having a Bachelor’s degree or higher (AOR = 5.66; 95% CI: 1.53–20.88). Conclusions: Oral hygiene among hospitalized patients in Al-Ahsa was inadequate, particularly in public hospitals where essential supplies were lacking. Hospitals should adopt clear oral care policies, ensure supply availability, train staff, and integrate dental professionals to improve patient safety and prevent complications.