Within the past decade, there has been a surge of interest in investigating the effects of clown intervention in a large variety of clinical settings. Many studies have focused on the effects of clown intervention on children. However, few studies have investigated clowning effects on adults. This paper presents an overview of the concept of medical clowning followed by a literature review conducted on the empirical studies drawn from three data bases (PubMed, PsycINFO, and Google Scholar), with the aim of mapping and discussing the evidence of clowning effects on non-children, namely adults. The following areas were investigated: Adult and elderly patients (mainly those with dementia), observers of clowning, namely non-hospitalized adults who are at the hospital as relatives of patients or health-care staff, and finally clowns themselves. The main results are that 1) clown intervention induces positive emotions, thereby enhancing the patient’s well-being, reduces psychological symptoms and emotional reactivity, and prompts a decrease in negative emotions, such as anxiety and stress; 2) clown doctors are also well-perceived by relatives and healthcare staff and their presence appears to be useful in creating a lighter atmosphere in the health setting; 3) few pilot studies have been conducted on clown doctors and this lacuna represents a subject for future research.