Background: Nosocomial infections, or healthcare-associated infections (HAIs), represent a significant global health challenge frequently associated with invasive medical procedures and extended hospitalizations. This study was designed to evaluate the current level of knowledge and the perceptions of inpatients regarding HAIs within a high-risk tertiary hospital in the Qassim region of Saudi Arabia. Method: A descriptive cross-sectional study was conducted from August 2024 to February 2025 at a tertiary facility in the Qassim region. The study population included 500 inpatients aged 18 years and older who consented to participate. Data were collected via individual interviews using a closed-ended questionnaire, which assessed demographics, knowledge and perceptions of HAIs on a 4-point Likert scale. Results: Among 500 study participants, good knowledge, fair knowledge and poor knowledge regarding HAIs were demonstrated by 57%, 38.4% and 4.6%, respectively. More than 98% of participants achieved a perception score of above 70%, indicating a profoundly positive perception level. Knowledge was significantly associated with age (p = 0.018), educational status (p < 0.01), and nationality (p < 0.01). Participants most commonly recognized contaminated hospital beds (95.6%), airborne transmission (91.2%), and unsterilized equipment (90%) as the potential modes of infection transmission. Conclusions: Sustaining ongoing infection prevention efforts and fostering improved awareness among inpatients regarding HAIs are of paramount importance in implementing effective public health prevention measures.