Background To develop and validate the American-English version of the self-reporting Acute Cystitis Symptom Score (ACSS), a suitable tool for diagnosis and patient-reported outcome in female patients with acute uncomplicated cystitis (UC). Methods After certified translation into American-English and cognitive assessment, the clinical validation of the ACSS was performed as an embedded study in a US phase II trial (ClinicalTrials.gov Identifier: NCT03129295). Results A total of 167 female patients with typical symptoms of UC were included in the study following FDA guidance. At Day 1 (diagnosis) the mean(SD) sum score of the six ACSS typical symptoms reached 10.60(2.51). Of 100 patients followed-up last time on Day 5 or 6 (End-of-treatment, EoT), 91 patients showed clinical success according to the favoured ACSS criteria (sum score of typical symptoms 0.98(1.94)). There was no correlation between the severity of symptoms on Day 1 or between clinical success rate at EoT and level of bacteriuria on Day 1. Conclusion The American-English ACSS showed high predictive ability and responsiveness, and excellent levels of reliability and validity. It can now be recommended as the new master version in clinical and epidemiological studies, in clinical practice or for self-diagnosis of women with symptoms of UC.