Introduction: Hard-flaccid syndrome is gaining increased interest among male sexual dysfunctions in the last years. It is poorly understood and defined. Most of the information comes from online forums. This paper is a review of current knowledge on the clinical presentation, diagnosis, pathophysiological mechanisms and treatments of this newly recognized condition.Material and methods: A literature review was conducted on MEDLINE, CENTRAL, PASCAL databases and google scholar, using the terms: hard, flaccid, syndrome. The research identified 16 articles published between 2018 and February 2019. After reference lists review and duplicates removal, 7 full text references were eligible and useful for our review that follows PRISMA guidelines.Results: The condition is acquired, chronic and painful. It is characterized by a constantly semi-rigid penis at the flaccid state and a loss in erectile rigidity. Patients have penile sensory changes, urinary symptoms, erectile dysfunction, pelvic floor muscles contraction and psychological distress. Symptoms are worse in standing position. The majority of the cases aged between their second and third decades. A traumatic injury at the base of an erect penis is the initial event. Neurovascular structures damage and subsequent sensory, muscular and vascular changes follow. Initial symptoms trigger emotional distress and reactional sympathetic stimulation that worsen symptoms. Diagnosis is based on patient's history. Imaging and blood tests are normal. Differential diagnosis includes high-flow priapism and non-erecting erections. A multimodal treatment has been so far the most beneficial strategy, consisting of behavioral modifications to reduce stress and decrease pelvic floor muscles contraction, evaluation and treatment of the associated psychological conditions, and medical therapy for pain control and the treatment of the associated erectile dysfunction.Conclusion: Hard-flaccid syndrome is poorly recognized in the daily clinical experience and not well defined. A multimodal approach seems so far the most efficient strategy for treatment. Additional evidence based studies with better quality are needed to define the exact pathophysiological mechanisms and subsequently more efficient therapeutic strategies.