Background: The NETTER-1 clinical trial showed that peptide receptor radionuclide therapy (PRRT) with ¹⁷⁷Lu-DOTATATE increased progression-free survival in patients with somatostatin-receptor-positive advanced midgut neuroendocrine tumors (NETs) compared with high-dose octreotide long-acting repeatable, and was associated with few serious adverse events (AEs). To assess the safety profile of ¹⁷⁷Lu-DOTATATE in a real-world population, we analyzed safety data from a US expanded access program (NCT02705313). Methods: Patients had inoperable, histologically proven, somatostatin-receptor-positive, locally advanced or metastatic GEPNETs (Ki-67 index ≤ 20%) that progressed after somatostatin analog therapy. Exclusion criteria were: surgery, radiotherapy or chemotherapy in the last 12 weeks; treatment with an interferon, mTOR inhibitor, or other systemic therapy in the last 4 weeks; or ongoing octreotide therapy that could not be interrupted for PRRT. Patients with impaired renal function (serum creatinine > 1.7 mg/dL or creatinine clearance < 50 mL/min) or serious coexisting conditions were excluded. The analysis included patients who received ≥ 1 cycle of ¹⁷⁷Lu-DOTATATE between July 5, 2016 and December 21, 2018. Data were collected from the first cycle to the latest data collection point (up to October 7, 2019). Results: 299 patients received a mean ¹⁷⁷Lu-DOTATATE cumulative dose of 552 mCi (20.4 GBq) (standard deviation [SD]: 220 mCi [8.1 GBq]) over a mean of 2.8 cycles (SD: 1.1). Mean age was 60.8 years (SD: 11.7); 38.5% of patients were men. Over a mean follow-up of 131 days (SD: 87), 48.8% of patients reported treatment-related AEs (TRAEs), with a maximum severity of grade 1, 2 and 3 for 26.8% (n = 80), 18.1% (n = 54) and 4.0% (n = 12) of patients, respectively; there were no grade 4–5 TRAEs. The most common TRAEs of any grade (≥ 5.0% of patients) were nausea (31.1%), vomiting (13.7%), fatigue (9.4%) and thrombocytopenia (6.0%). The most prevalent grade 3 TRAEs were lymphocyte count decrease (1.0%) and thrombocytopenia (0.7%). Serious TRAEs occurred in 1.0% of patients (carcinoid crisis, dehydration, syncope and vomiting). AEs led to dose modification in 1.7% of patients, dose delay in 6.4% (most commonly due to nausea [2.0%] or thrombocytopenia [2.0%]) and discontinuation in 1.3% (due to thrombocytopenia [1.0%] and extravasation [0.3%]). Conclusions: In a real-world population of US patients with advanced GEPNETs, ¹⁷⁷Lu-DOTATATE treatment was well tolerated with few TRAEs, consistent with the safety profile in the NETTER-1 trial. Clinical trial information: NCT02705313.