Many studies have described the frequency of short-term complications in patients undergoing first rib resection for thoracic outlet syndrome (TOS). The rate of long-term complications is less well known. 699 patients that had undergone first rib resection for TOS during 2004–2018 were identified from the Care Register for Healthcare in Finland. The prevalence of complications within 30 days and 1 year was analyzed. The prevalence of complications within 30 days was 9.8%, and complications occurred in 18.8% of the cases within 1 year. The rate of vascular and neural complications increased from 5.9% and 0.7% within 30 days to 10.3% and 2.7% within 1 year, respectively. Only a slight increase was seen in the rate of pneumo/chylothorax or infection. A follow-up of at least 1 year is prudent to detect all complications in patients undergoing first rib resection for TOS.