Clinical practice guidelines (CPGs) are intended to support clinical decisions and should be based on high-quality evidence. Theobjective of the study was to evaluate the quality of evidence supporting the recommendations issued in CPGs for therapy,diagnosis, and prevention of hospital-acquired and ventilator-associated pneumonia (HAP/VAP). CPGs released by internationalscientific societies after year 2000, using the Grades of Recommendation, Assessment, Development, and Evaluation (GRADE)methodology, were analyzed. Number and strength of recommendations and quality of evidence (high, moderate, low, and verylow) were extracted and indexed in the aforementioned sections. High-quality evidence was based on randomized control trials(RCT) without important limitations and exceptionally on rigorous observational studies. Eighty recommendations wereassessed, with 7 (8.7%), 24 (30.0%), 29 (36.3%), and 20 (25.0%) being supported by high, moderate, low, and very lowquality evidence, respectively. Highest evidence degree was reported for 26 prevention recommendations, with 7 (26.9%)supported by high-quality evidence and no recommendation based on very low-quality evidence. In contrast, among 9 recommendations for diagnosis and 45 for therapy, none was supported by high-quality evidence, in spite of being recommended asstrong in 33.3% and 46.7%, respectively. Among HAP/VAP diagnosis recommendations, the majority of evidence was rated as low or very low-quality (55.6% and 22.2%, respectively) whereas among HAP/VAP therapy recommendations, 4/5 were rated aslow and very low-quality (40% each). In conclusion, among HAP/VAP international guidelines, most recommendations, particularly in therapy, remain supported by observational studies, case reports, and expert opinion. Well-designed RCTs are urgently needed.