Purpose Guidelines generally do not recommend oral antimicrobials for prophylaxis against chemotherapy-related infections in patients with solid tumors. Evidence on antimicrobial prophylaxis use, and associated chemotherapy-related infection risk, in US clinical practice is limited. Methods A retrospective cohort design and data from two US private healthcare claims repositories (2008-2011) were employed. Study population included adults who received myelosuppressive chemotherapy for non-metastatic cancer of the breast, colon/rectum, or lung, or for non-Hodgkin’s lymphoma. For each subject, the first chemotherapy course was characterized, and within the first course, each chemotherapy cycle and chemotherapy-related infection episode was identified. Use of prophylaxis with oral antimicrobials and colony-stimulating factors in each cycle also was identified. Results A total of 7116 (22% of all) non-metastatic breast cancer, 1833 (15%) non-metastatic colorectal cancer, 1999 (15%) non-metastatic lung cancer, and 1949 (21%) non-Hodgkin’s lymphoma patients received antimicrobial prophylaxis in ≥1 cycle. Mean number of antimicrobial prophylaxis cycles during the course among these patients was typically <2, with little difference across cancers and chemotherapy regimens. Fluoroquinolones were the most commonly received class of antimicrobials, accounting for 20%-50% all antimicrobials administered. Among subjects who received first-cycle antimicrobial prophylaxis, chemotherapy-related infection risk in that cycle ranged from 3% to 6% across cancer types. Among patients who received first-cycle antimicrobial prophylaxis and developed chemotherapy-related infections, 38%-67% required inpatient care. Chemotherapy-related infection risk in subsequent cycles with antimicrobial prophylaxis was comparable. Conclusion The results of this study suggest that use of antimicrobial prophylaxis during myelosuppressive chemotherapy is far from uncommon in clinical practice. The results also suggest that an important minority of cancer chemotherapy patients receiving antimicrobial prophylaxis still develop serious infection requiring hospitalization.