Lymphedema is a lifetime complication of breast cancer survivors that can limit their participation in recreational or strenuous daily activities. Follow-up of lymphedema using an Internet application could help patients to determine the influence on their condition of these activities and adapt them accordingly. We aimed to determine the level of agreement between lymphedema assessment by telerehabilitation and by the traditional face-to-face method. Thirty breast cancer survivors participated in a descriptive study of repeated measures using a crossover design. Patients attended a session for clinical face-to-face and real-time online telerehabilitation assessments of lymphedema. There was a 120-min interval between these two sessions. The order of sessions was randomly selected for each patient. A caregiver (relative or friend) conducted the telerehabilitation assessment using a system that includes a specific tool based on an arm diagram for measuring the participant's arm circumferences via a telehealth application. All outcome measures showed reliability estimates (α) ≥ 0.90; the lowest reliability was obtained for the total volume on the non-affected side (α = 0.90). The diagnosis of lymphedema by the two methods also showed good inter-rater reliability (Rho = 0.89). These preliminary findings support the use of an Internet-based system to assess lymphedema in breast cancer survivors, offering carers a useful role in helping patients to follow up this lifetime health problem.