Background: Osteosarcoma (OS) is most common in the pediatric (ped) and young adult population but can occur at any age. Amongst other factors, older age confers a worse prognosis, and it is uncertain whether this is due to inherent biologic differences or treatment approaches. Lung-only metastases (mets) is common, and metastasectomy is performed frequently to improve overall survival. Little is known about the differences in lung-only metastatic OS and approaches to metastasectomies between ped and adult populations. Methods: A single-institution retrospective chart review using a free-text search engine and keywords “osteosarcoma, “lung mets” and “pulmonary mets”, generated 206 patients(pts) diagnosed from 2006-2021. Eligible pts had a diagnosis of lung-only metastatic disease, resection performed at the institution and at least one year of follow-up data. Data was analyzed in two cohorts based on age at OS diagnosis: ped (age<18) and adult (age > 18 years), as well as with age as a continuous predictor. Results: Fifty pts (27F/23M) with lung only mets were eligible for analysis with a median follow up of 10.4 years. Median age was 23 yrs (range 6-77); 20 pts (40% were ≤18 years old); 31 pts (16 ped, 15 adult) had an extremity primary site. Rates of metachronous (67% vs 60%) and bilateral (50% vs 40%) lung mets were similar in ped vs. adult pts, respectively. The median number of lung mets was 2 (range 1 to > 25) with 50% of patients (35) having 2-6 metastases (8 ped, 20 adult). The median size of lung metastasis was 1.2 cm (range 0.1-4.0 cm). 15 ped pts (75%) underwent metastasectomy, compared to 19 adult (63.3%) (OR 1.74, p = 0.39). Probability of metastasectomy decreased with age when used as a continuous predictor (p = 0.11). Ped pts were more likely to have an open procedure as compared to thoracoscopic (OR 12.75, p < 0.01). There was no significant difference in relapse-free survival between ped and adult pts who underwent metastatectomy (p = 0.84). Median overall survival following lung metastasis detection was 5.8 years for ped pts compared to 3 years for adult pts (p = 0.15 from Cox model). Conclusions: Multiple tumor and patient-specific factors affect the decision to undergo metastatectomy in lung-only OS. In our single-center study we learned that timing, pattern, and number of lung mets in ped vs. adult pts were similar, but younger pts were more likely to undergo an open procedure. Our data trended towards a lower chance of undergoing metastatectomy with older age. Larger studies are required to further understand decision-making and therapeutic outcome and a randomized study of open vs. thoracoscopic metastatecomy for lung-only OS mets is underway. In this small study, many patients with lung-only metastatic OS had long-term survival. We showed that relapse-free survival post-metastatecomy was similar in ped and adult patients.