This study was undertaken to describe the relationship between the occurrence and timing of neutropenic events and chemotherapy treatment in a community-based population of patients with cancer. The study included 2962 patients with breast, lung, colorectal, lymphoma, and ovarian cancers from a prospective U.S. registry of patients initiating a new chemotherapy regimen. Detailed patient-, disease-, and treatment-related data, including toxicities, were captured at baseline, the beginning of each cycle, and each midcycle blood draw for up to 4 cycles of treatment. Primary outcomes included febrile neutropenia (FN), severe neutropenia without fever/infection, and relative dose intensity (RDI). Thirty-seven percent of patients were aged 65 years or older, 43.5% had an Eastern Cooperative Oncology Group performance status of 1 or greater, and 27% had 1 or more comorbidities. Reductions in RDI to less than 85% of standard in the first cycle were planned in 23.6% of patients, whereas primary colony-stimulating factor prophylaxis was used in 18.2%. In the first 3 cycles of treatment, 10.7% of patients experienced FN, with most of these events (58.9%) occurring in the first cycle. This first-cycle pattern was consistently observed despite wide variations in event rates by tumor type, disease stage, chemotherapy regimen and dose, and patient characteristics. Despite frequent planned reductions from standard RDI, the incidence of FN remains high in community oncology practice in the United States. Improved methods of pretreatment assessment of patient risk factors for neutropenia are needed.