Urethral swabs are still currently used as a diagnostic tool when urethritis or prostatitis are suspected. Urologists are certainly aware that Peyronie's disease may occur after traumatic urethral instrumentation (catheterization, urethrocystoscopy, etc), but onset of Peyronie's disease after urethral swab for diagnostic purposes has never been reported in the literature. This paper presents the case of a patient who developed Peyronie's disease after a clumsy urethral swab insertion. It is an unusual, and to date unreported, complication which we would like to call attention to. In the case of our patient, the swab had been inserted to a greater depth than normally required and strong pressure had also been applied. During the procedure, the patient experienced severe urethral and penile pain, which was followed by urethrorrhagia, and later penile curvature. The patient was treated conservatively with good results, partly because the disease was still in its active stage and not yet stable. In the light of what we report, when ordering a urethral swab, physicians should always recommend that it be performed at testing centers that follow accurate, rigorous standards. Patients should also be informed that the test they are to undergo consists of a swab being inserted into the urethra for a short distance, not more than 2-3 cm.