Background: There have been significant therapeutic advances for HER2+ metastatic breast cancer (MBC) over the past decade. The aim of this study was to evaluate prognostic factors in metastatic HER2+ disease and their relationship with short- and long-term overall survival (OS) in the modern era. Methods: We evaluated patients (pts) with de novo metastatic HER2+ breast cancer diagnosed between years (y) 2010 and 2018, reported in SEER. Univariate analyses were performed to determine the effect of each variable on OS. Significant variables were included in a multivariate Cox model for OS that evaluated all pts diagnosed 2010 – 2018. Univariate and multivariate logistic regression was used to evaluate the association of each variable with short (< 2 y) and long (≥ 5 y) term OS. To allow sufficient follow up, only pts diagnosed 2010 – 2016 were included in the logistic regression for OS < 2 y, and only those diagnosed 2010 – 2014 were included for OS ≥ 5 y. Results: We included 5,576 pts with a median follow up of 48 months (IQR 25 – 73 months). Median OS was 41 months. The proportion alive at 2 y, 5 y, and 8 y, was 63.3% (95% CI 62.0% - 64.7%), 37.8% (95% CI 36.2% - 39.4%) and 26.8% (95% CI 24.8% - 28.9%), respectively. In multivariate analysis for OS, older vs younger age (HR 2.5), black vs white pts (HR 1.4), non-ductal non-lobular vs ductal (HR 2.7), bone metastases vs not (HR 1.2), brain metastases vs not (HR 1.8), liver metastases vs not (HR 1.6), lung metastases vs not (HR 1.3), 6 metastatic organ sites vs 1 (HR 3.6), ER/PR- vs + (HR 1.3), < $35k income vs ≥ $75k (HR 1.8), and being diagnosed in earlier years (HR 1.06 per each prior year) had significantly worse OS (all p≤0.044). Similar results were seen for breast cancer-specific survival. Factors associated with < 2 y OS in adjusted models were older age (OR 3.8), black race (OR 1.5), non-ductal non-lobular (OR 4.6), brain metastases (OR 3.0), liver metastases (OR 2.0), lung metastases (OR 1.6), ER/PR- (OR 1.7) and lower income (OR 1.6), all p < 0.04. Number of metastatic organ sites was not significant in this model. Factors associated with ≥ 5 y OS in adjusted models were younger age (OR 2.9), white vs black race (OR 1.7), fewer metastatic organ sites (OR 2.6), ER/PR+ (OR 1.3), and higher income (OR 3.3), all p < 0.02. Specific organ sites (bone, brain, liver and lung) were not significant in this model. Conclusions: In this cohort of pts with de novo HER2+ MBC, OS improved significantly over the study period, and a considerable proportion of pts were still alive at 8 y. Factors associated with shorter survival included older age, black race, lower income, and the presence of visceral or brain metastases. Long-term (≥ 5 y) survival was associated with both demographic (younger age, white race, higher income) and tumor-related (fewer metastatic sites, ER/PR positivity) factors.