Background: The COVID-19 pandemic was associated with declines in in-person clinical visits. While telemedicine visits have increased, uptake has varied. Here we assess demographic and socioeconomic factors associated with telemedicine use among patients initiating treatment for 21 common cancers at community oncology clinics. Methods: This retrospective study uses the nationwide Flatiron Health electronic health record-derived de-identified database of patients with cancer. Patient characteristics were determined using structured and unstructured data curated via technology-enabled abstraction. We included patients (≥ 18 years) who initiated first-line cancer treatment between March 2020 and September 2021 (follow-up through December 2021). We focused on differences in telemedicine use (≥ 1 telemedicine visit within 90 days after treatment initiation) across race/ethnicity, insurance coverage, rurality (per Rural-Urban Commuting Areas), and socioeconomic status (SES). SES was defined using census block group data from the American Community Survey (2015-2019) (quintiles representing least to most affluent areas) based on patient addresses and measured using the Yost Index (incorporating income, home values, rental costs, poverty, blue-collar employment, unemployment, and education information). We used logistic regression models adjusted for clinical characteristics (i.e., age, sex, performance status, and stage) to examine differences in telemedicine use. Results: This study included 24,164 patients (48.1% women, median age: 69 [interquartile range: 61-77] years), of whom 15.9% used telemedicine services. Black patients were less likely to use telemedicine services than White patients (11.4% vs. 15.6%, odds ratio [OR] 0.69 [95% confidence interval [CI]: 0.59-0.79], p<0.01). Telemedicine use was also lower among patients without documented insurance than well-insured (commercial and Medicare payers) patients (10.7% vs. 15.9%, OR 0.62 [95% CI: 0.54-0.72], p<0.01). Those in rural (9.8%, OR 0.51 [95% CI: 0.45-0.58], p<0.01) and suburban areas (13.1%, OR 0.71 [95%: 0.64-0.79], p<0.01) were less likely to use telemedicine services than patients in urban areas (17.6%). Finally, patients in the least affluent areas had lower telemedicine use than those in the most affluent areas (10.2% vs. 24.3%, OR 0.35 [95% CI: 0.31-0.40], p<0.01). Conclusions: During the COVID-19 pandemic, nearly one-fifth of patients initiating cancer treatment used telemedicine services. However, there were substantial disparities: Black, uninsured, non-urban, and less affluent patients are less likely to use telemedicine services. While telemedicine may expand access to specialty care, the proliferation of these services may widen cancer care disparities if vulnerable populations do not have equitable access.