Incidence and manifestations of postacute sequelae of coronavirus disease 2019 (PASC) are poorly defined among immunosuppressed populations. We reported, phenotyped, and assessed risk factors for PASC in adults with systemic autoimmune diseases. Persons aged ≥ 18 years with systemic autoimmune diseases were recruited into a national, prospective observational cohort of SARS-CoV-2 vaccination and infection between December 2020 and April 2021. Serial surveys assessed vaccination status, SARS-CoV-2 infection incidence, and disease flares. Participants reporting SARS-CoV-2 infection received a questionnaire assessing symptom duration, severity, and quality of life (QOL) effect; PASC was defined as ≥ 1 symptom persisting for > 12 weeks. PASC syndromes were mapped by overlapping symptom domains. Characteristics were compared between participants who did vs did not report PASC. Among 1615 participants, 590 (36.5%) reported SARS-CoV-2 infection and were sent PASC surveys, 299 (50.7%) of whom responded > 12 weeks following the reported infection. Respondents were 91.6% female, 91.2% White, median (IQR) age was 48 (40-60) years with median (IQR) 3 (2-3) vaccine doses at time of first infection. Common diagnoses included inflammatory arthritis (38.5%) and inflammatory bowel disease (14.4%). Eighty-nine of 299 (29.8%) reported PASC, with the most reported symptom domain being neurological/psychological (83.1%); 84% reported an effect on QOL. Participants with PASC reported lower number of preceding vaccines (median [IQR] 2 [2-3] vs 3 [2-3]; P < 0.001) and more reinfections (16.9% vs 5.7%; P = 0.004). In a large, real-world cohort, 29.8% of persons with systemic autoimmune disease reported PASC, often affecting QOL. Preceding vaccination may reduce PASC, whereas multiple infections may increase risk, supporting ongoing booster vaccine campaigns and efforts to limit breakthrough infections.