Objective: To determine how clinical and laboratory factors were associated with nosocomial pneumonia in adult patients hospitalized in an internal medicine department. Methods: We conducted a retrospective unmatched case-control study. We recorded clinical and epidemiological data from patients discharged from an internal medicine department of a Peruvian reference hospital, the Hospital Nacional Arzobispo Loayza, between 2016 and 2018. Bivariate and multivariate analyses (using logistic regression models) were performed to obtain crude and adjusted odds ratios with 95% confidence intervals. A P value < 0.05 was considered significant. We calculated the population attributable fraction of the significant variables. Results: We analyzed 138 cases and 200 controls, with a mean age of 72.6 ± 17.8 years (21 to 104) for cases and 71.7 ± 15.3 years (19 to 98) for controls. The multivariate analysis indicated that severe anemia (adjusted odds ratio 9.0, confidence interval 95% 1.9 to 43.1, P = 0.01), severe hypoalbuminemia (adjusted odds ratio 4.0, confidence interval 95% 1.2 to 13.8, P = 0.03), altered state of consciousness (adjusted odds ratio 3.6, confidence interval 95% 1.6 to 8.2, P = 0.00), and prior use of antibiotics (adjusted odds ratio 6.3, confidence interval 95% 2.7 to 14.5, P = 0.00) were significantly associated with nosocomial pneumonia. The population attributable fraction found were 41.8% for altered state of consciousness, 33.2% for severe anemia, and 36.3% for severe hypoalbuminemia. Conclusion: Clinical and laboratory risk factors associated with nosocomial pneumonia development in adult patients hospitalized in an internal medicine department were severe anemia, severe hypoalbuminemia, altered consciousness, and previous use of antibiotics.