Objective: Human immunodeficiency virus (HIV) prevention efficacy trials with psychiatric patients have been conducted in research settings in high-resourced countries, establishing short-term efficacy for reducing sexual risk behavior. None has been implemented within systems of care. In the last decade, overcoming this research-to-practice gap has become a focus of implementation science. This paper describes the first and only HIV Prevention intervention trial for psychiatric patients conducted in real-world outpatient psychiatric settings facilitated by trained clinic-based providers. Methods: The HIV Prevention intervention, which uses the Information-Motivation-Behavioral Skills model to achieve sexual risk-reduction, was rigorously adapted to the local context and clinic services’ needs. Participants from eight clinics were randomized to HIV Prevention or Health Promotion conditions. Results: HIV Prevention participants showed significant improvement in Information-Motivation-Behavioral domains; in this group, behavioral intentions were associated with significantly fewer unprotected sex occasions, but reduction of unprotected sex occasions was similar in both conditions. Conclusion: Our trial was conducted before implementation studies became widely funded. Transporting an intervention to a new culture or into real-world practice settings may require adaptations. Our results demonstrate that clear guidelines are needed regarding whether to conduct efficacy, effectiveness, and/or implementation research as the most appropriate next step. Clinical trial registration: NCT00881699

Differing from the studied Eutheria the white belly opossum Peyer"s patches do not present a conspicous dome. M cells are located in the inmer layer of bilaminal invaginations formed at the bottom of the villi. A great variation in the morphology of M cells was observed. The enterocytes located at the epithelial inner layer may present endocytic vesicles, and the microvilli are shorter tha the microvilli of enterocytes lining the small intestine. As these morphological aspects have been described to exist in the enterocytes of the lancet opossum small intstine it was surmised that the opossum Peyer's patches special epithelium could represent the persistence in adult animals of a cellular pattern established before the intestinal maturation had occurred.