Objectives:  Botulinum toxin type A (BoNT/A) proved very effective in therapy for hyperactive detrusor or sphincter dysfunction of neurogenic and non‐neurogenic origin. However, therapy may fail. In a search for possible reasons, we investigated the presence of BoNT/A antibodies (BoNT/A‐AB) in patients who were treated more than once and correlated the presence of antibodies with clinical findings.Methods:  In 25 patients (aged 11–75 years; average, 48.3 years) who had experienced at least one previous BoNT/A detrusor and/or sphincter injection, BoNT/A‐AB was detected with the mouse diaphragm assay before and within 3 months after the current injection. Clinically, subjective and objective outcomes of this injection session were determined on an efficacy scale.Results:  In eight patients, BoNT/A‐AB was detected; titers were clearly positive in four patients and were borderline in four patients. The subjective and objective outcomes indicated complete therapy failure in three of four patients who were positive for BoNT/A‐AB. In two patients, BoNT/A‐AB developed after just one injection session.Conclusions:  Botulinum toxin type A antibodies can develop after injection of BoNT/A for urologic disorders and the antibodies can lead to therapy failure. In patients with clinically complete therapy failure in whom no obvious other causes can be determined (such as a progressive disease in a patient with multiple sclerosis), screening for BoNT/A‐AB should be carried out.