ObjectivePatients with chronic rheumatic diseases (CRDs), such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA), require special attention during the COVID‐19 pandemic as they are considered at risk of severe infections. Our objective was to assess the seroprevalence of SARS–CoV‐2 in patients with SLE and RA and to assess patient behavior, disease‐related symptoms, and mental health.MethodsMore than 900 participants were included: 405 patients with RA or SLE (CRD patients) and 513 blood donors. All participants had blood SARS–CoV‐2 total antibodies measured (sensitivity 96.7%, specificity 99.5%) and answered a questionnaire concerning behavior, anxiety, and symptoms of depression (Patient Health Questionnaire 9). The CRD patients were further asked about physical activity, adherence to medication, and disease‐related symptoms.ResultsCRD patients had a significantly lower seroprevalence of SARS–CoV‐2 antibodies (n = 1 of 365, 0.3%) compared to blood donors (n = 10 of 513, 1.9%; P = 0.03). Almost 60% of patients were unable to exercise as usual, and increased pain and disease activity was experienced by 34% and 24% of patients, respectively. Almost 10% of patients reduced or discontinued their immunosuppressive treatments at their own initiative. Symptoms of moderate depression were present in 19% of patients compared to 6.8% of blood donors (P < 0.001).ConclusionLow seroprevalence in patients with CRDs indicates successful mitigation of exposure to SARS–CoV‐2. However, this mitigation appears to occur at the expense of physical activity, experience of increased pain, disease activity, and symptoms of depression. There is a need for care providers to be aware of these negative side effects and for further studies to investigate the possible long‐term consequences.