To develop and implement a continuing professional development (CPD) activity focused on geriatric assessment (GA) in oncology for oncologists and geriatricians. We evaluated the impact of this activity on knowledge, skills, and performance regarding GA in oncology, as well as its feasibility and acceptability. We included teams composed of an oncologist and a geriatrician working in Mexico. Curriculum content was selected from geriatric oncology guidelines. We used Project Extension for Community Healthcare Outcome (ECHO)'s model to create a 12-week online course. A one-group pretest post-test quasi-experimental design was used to evaluate the intervention's effectiveness. At baseline, participants answered a multiple-choice knowledge assessment, a survey on self-perceived competence in GA, and an adaptation of the Association for Community Cancer Centers Geriatric Oncology Gap Assessment Tool, evaluating self-perceived performance in conducting geriatric interventions. These assessments and a satisfaction questionnaire were also completed postintervention. Baseline and postintervention scores were compared using paired t-tests. We included 40 participants (20 oncologists and 20 geriatricians). Median attendance was 10 sessions (range 2-12). Thirty-eight participants completed the satisfaction questionnaire, with a median score of 10/10 (range 8-10). The mean baseline and postintervention knowledge scores were 59.5 ± 12.8 and 74.4 ± 9.7, respectively (P < .001, effect size 1.14). The mean baseline and postintervention competence scores were 6.42 ± 2.5 and 9.02 ± 0.8, respectively (P < .001, effect size 1.03). The mean baseline and postintervention performance scores were 2.58 ± 0.65 and 3.29 ± 0.5, respectively (P < .001, effect size 1.64). A CPD activity for oncologists and geriatricians on the basis of the Project ECHO model was feasible and acceptable, leading to increased knowledge, competence, and performance in geriatric oncology. This could represent a novel method for increasing the geriatric competence of the cancer care workforce in Latin America and globally.