High-grade gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs, G3) are aggressive cancers of the digestive system with poor prognosis and survival. Platinum-based chemotherapy (cisplatin/carboplatin + etoposide) is considered the first-line palliative treatment. Etoposide is frequently administered intravenously; however, oral etoposide may be used as an alternative. Concerns for oral etoposide include decreased bioavailability, inter- and intra-patient variability and patient compliance. We aimed to evaluate possible differences in progression-free survival (PFS) and overall survival (OS) in patients treated with oral etoposide compared to etoposide given as infusion. Patients (n = 236) from the Nordic NEC study were divided into three groups receiving etoposide as a long infusion (24 h, n = 170), short infusion (≤ 5 h, n = 33) or oral etoposide (n = 33) according to hospital tradition. PFS and OS were analyzed with Kaplan-Meier (log-rank), cox proportional hazard ratios and confidence intervals. No statistical differences were observed in PFS or OS when comparing patients receiving long infusion (median PFS 3.8 months, median OS 14.5 months), short infusion (PFS 5.6 months, OS 11.0 months) or oral etoposide (PFS 5.4 months, OS 11.3 months). We observed equal efficacy for the three administration routes suggesting oral etoposide may be safe and efficient in treating high-grade GEP-NEN, G3 patients scheduled for cisplatin/carboplatin + etoposide therapy.