Background: Coronavirus disease 2019 (COVID-19) patients on haemodialysis (HD) have high mortality. We investigated the value of reverse transcription polymerase chain reaction (RT-PCR) and the dynamic changes of antibodies (enzyme-linked immunosorbent assay immunoglobulin M (IgM) + IgA and/or IgG) in a large HD cohort. Methods: We conducted a prospective observational study in 10 Madrid HD centres. Infection rate, anti-SARS-CoV-2 antibody dynamics and the incidence of asymptomatic SARS-CoV-2 infection (defined by positive RT-PCR, IgM + IgA and/or IgG) were assessed. Results: From 1 March to 15 April 2020, 136 of 808 (16.8%) HD patients were diagnosed with symptomatic COVID-19 by RT-PCR of nasopharyngeal swabs and 42/136 (31%) died. In the second fortnight of April, RT-PCR and anti-SARS-CoV-2 antibodies were assessed in 763 of the surviving patients. At this point, 69/91 (75.8%) symptomatic COVID-19 patients had anti-SARS-CoV-2 antibodies. Four weeks later, 15.4% (10/65) of initially antibody-positive patients had become negative. Among patients without prior symptomatic COVID-19, 9/672 (1.3%) were RT-PCR positive and 101/672 patients (15.0%) were antibody positive. Four weeks later, 62/86 (72.1%) of initially antibody-positive patients had become negative. Considering only IgG titres, serology remained positive after 4 weeks in 90% (54/60) of patients with symptomatic COVID-19 and in 52.5% (21/40) of asymptomatic patients. The probability of an adequate serologic response (defined as the development of anti-SARS-CoV-2 antibodies that persisted at 4 weeks) was higher in patients who had symptomatic COVID-19 than in asymptomatic SARS-CoV-2 infection {odds ratio [OR) 4.04 [95% confidence interval (CI) 2.04-7.99]} corrected for age, Charlson comorbidity index score and time on HD. Living in a nursing home [OR 5.9 (95% CI 2.3-15.1)] was the main risk factor for SARS-CoV-2 infection. Conclusions: The anti-SARS-CoV-2 antibody immune response in HD patients depends on clinical presentation. The antibody titres decay earlier than previously reported for the general population. This inadequate immune response raises questions about the efficacy of future vaccines.