Irregular practitioners (‘quacks’) specialising in male sexual problems succeeded in nineteenth-century New Zealand by taking advantage of the growing population of unattached men who were ignorant of their own sexual physiology. The irregulars also profited from the regular practitioners’ acceptance of ill-defined or imaginary male sexual disorders and the side effects of conventional venereal disease treatments, the lack of a clear demarcation between quacks and the regular medical profession, and an increased availability of newspaper advertising. Improvements in the postal system enabled quacks to reach more potential customers by mail, their preferred sales method. The decline in quackery resulted from scientific advances in the understanding of disease and government legislation to privilege regular practitioners and limit quacks’ access to postal services and advertising.