We sought to describe contemporary presentation, treatment, and outcomes of patients presenting with acute (A), perforated (P), and gangrenous (G) appendicitis in the United States. Recent European trials have reported that medical (antibiotics only) treatment of acute appendicitis is an acceptable alternative to surgical appendectomy. However, the type of operation (open appendectomy) and average duration of stay are not consistent with current American practice and therefore their conclusions do not apply to modern American surgeons. This multicenter prospective observational study enrolled adults with appendicitis from January 2017 to June 2018. Descriptive statistics were performed. P and G were combined into a "complicated" outcome variable and risk factors were assessed using multivariable logistic regression. A total 3597 subjects were enrolled across 28 sites: median age was 37 (27-52) years, 1918 (53%) were male, 90% underwent computed tomography (CT) imaging, 91% were initially treated by appendectomy (98% laparoscopic), and median hospital stay was 1 (1-2) day. The 30-day rates of Emergency Department (ED) visit and readmission were 10% and 6%. Of 219 initially treated with antibiotics, 35 (16%) required appendectomy during index hospitalization and 12 (5%) underwent appendectomy within 30 days, for a cumulative failure rate of 21%. Overall, 2403 (77%) patients had A, whereas 487 (16%) and 218 (7%) patients had P and G, respectively. On regression analysis, age, symptoms >48 hours, temperature, WBC, Alvarado score, and appendicolith were predictive of "complicated" appendicitis, whereas co-morbidities, smoking, and ED triage to appendectomy >6 hours or >12 hours were not. In the United States, the majority of patients presenting with appendicitis receive CT imaging, undergo laparoscopic appendectomy, and stay in the hospital for 1 day. One in five patients selected for initial non-operative management required appendectomy within 30 days. In-hospital delay to appendectomy is not a risk factor for "complicated" appendicitis.