The present study aims to evaluate the diagnostic yield of bronchoalveolar lavage (BAL) fluid in patients with hematological malignancies and describe the most common pathogens detected in BAL fluid (BALF.) An analysis of 480 BALF samples was performed in patients with hematological malignancies over a period of 7 years. The results of culture methods, PCR, and immunoenzymatic sandwich microplate assays for Aspergillus galactomannan (GM) in BALF were analyzed. Further, the diagnostic thresholds for Aspergillus GM and Pneumocystis jiroveci were also calculated. Microbiological findings were present in 87% of BALF samples. Possible infectious pathogens were detected in 55% of cases; 32% were classified as colonizing. No significant difference in diagnostic yield or pathogen spectrum was found between non-neutropenic and neutropenic patients. There was one significant difference in BALF findings among intensive care units (ICU) versus non-ICU patients for Aspergillus spp. (22% versus 9%, p = 0.03). The most common pathogens were Aspergillus spp. (n = 86, 33% of BAL with causative pathogens) and Streptococcus pneumoniae (n = 46, 18%); polymicrobial etiology was documented in 20% of cases. A quantitative PCR value of > 1860 cp/mL for Pneumocystis jirovecii was set as a diagnostic threshold for pneumocystis pneumonia. The absorbance index of GM in BALF of 0.5 was set as a diagnostic threshold for aspergillosis. The examination of BAL fluid revealed the presence of pathogen in more than 50% of cases and is, therefore, highly useful in this regard when concerning pulmonary infiltrates.