Objectives: The primary aim was to assess patient-reported outcomes >= 1 year following a humeral diaphyseal fracture. The secondary aim was to compare outcomes of patients who united after initial management (operative/nonoperative) with those who united after nonunion fixation (NU-ORIF). Design: Retrospective. Setting: University teaching hospital. Patients and intervention: From 2008 to 2017, 291 patients [mean age, 55 years (17-86 years), 58% (n = 168/291) female] were available to complete an outcomes survey. Sixty-four (22%) were initially managed operatively and 227 (78%) nonoperatively. After initial management, 227 (78%) united (n = 62 operative, n = 165 nonoperative), 2 had a delayed union (both nonoperative), and 62 (21%) had a nonunion (n = 2 operative, n = 60 nonoperative). Fifty-two patients (93%, n = 52/56) united after NU-ORIF. Main Outcome Measures: QuickDASH, EuroQol-5 Dimension (EQ-5D)/EuroQol-Visual Analogue Scale (EQ-VAS), 12-item Short Form Physical (PCS) and Mental Component Summary (MCS). Results: At a mean of 5.5 years (range, 1.2-11.0 years) postinjury, the mean QuickDASH was 20.8, EQ-5D was 0.730, EQ-VAS was 74, PCS was 44.8 and MCS was 50.2. Patients who united after NU-ORIF reported worse function (QuickDASH, 27.9 vs. 17.6; P = 0.003) and health-related quality of life (HRQoL; EQ-5D, 0.639 vs. 0.766; P = 0.008; EQ-VAS, 66 vs. 76; P = 0.036; PCS, 41.8 vs. 46.1; P = 0.036) than those who united primarily. Adjusting for confounders, union after NU-ORIF was independently associated with a poorer QuickDASH (difference, 8.1; P = 0.019) and EQ-5D (difference, -0.102; P = 0.028). Conclusions: Humeral diaphyseal union after NU-ORIF resulted in poorer patient-reported outcomes compared with union after initial management. Targeting early operative intervention to at-risk patients may mitigate the potential impact of nonunion on longer-term outcome.