Abstract Background Postoperative home monitoring could potentially detect complications early, but evidence in oncogeriatric surgery is scarce. Therefore, we evaluated whether post-discharge physical activity, vital signs, and patient-reported symptoms are related to post-discharge complications and hospital readmissions in older patients undergoing cancer surgery. Methods In this observational cohort study, we monitored older patients (≥65 years of age) undergoing cancer surgery, for 2 weeks post-discharge using tablet-based applications and connected devices. Outcome measures were post-discharge complications and readmissions; physical activity and patient-reported symptoms over time; and threshold violations for physical activity (step count <1000 steps/day), vital signs (temperature <36°C or >38°C; blood pressure <100/60 mmHg or >150/100 mmHg; heart rate <50 bpm or >100 bpm; weight −5% or +5% of weight at discharge); and patient-reported symptoms (pain score greater than the previous day; presence of dyspnea, vomiting, dizziness, fever). Results Of 58 patients (mean age 72 years), 24 developed a post-discharge complication and 13 were readmitted. Measured parameters indicated 392 threshold violations out of 5379 measurements (7.3%) in 40 patients, mostly because of physical inactivity. Patients with readmissions had lower physical activity at discharge and at day 9 after discharge and violated a physical activity threshold more often. Patients with post-discharge complications had a higher median pain score compared with patients without these adverse events. No differences in threshold violations of other parameters were observed between patients with and without post-discharge complications and readmissions. Conclusion Our results show the potential of telemonitoring older patients after cancer surgery but confirm that detecting post-discharge complications is complex and multifactorial.