A small group of youth and emerging adults deals with severe and enduring mental health problems (SEMHP). Current mental health care struggles to recognize and treat this group timely and adequately, leaving these youth between the cracks of the system. A first step to improve care for this group is to gain a deeper understanding of the characteristics of youth with SEMHP. Therefore, this study aimed at reviewing current literature about this target group and what is known so far about their characteristics. We included 39 studies with a focus on youth aged 12–25 years with SEMHP. After critical appraisal, a content analysis and in-depth thematic analysis were conducted. According to the included studies, youth with SEMHP were characterized by severe distress and recurrent comorbid mental health problems, with pervasive suicidality. Further, underlying trauma, family conflicts, peer rejection, deep feelings of hopelessness, and psychosocial malfunctioning characterized SEMHP. It was described that for youth with SEMHP a pervasive pattern of dysfunction in multiple domains is present leading to a detrimental impact. Subsequently, this pattern exerts a reciprocal influence on the mental health problems, causing a vicious circle further worsening SEMHP. Our findings emphasize the need for a holistic approach and to look beyond the traditional classification system in order to meet the needs of these youth with wide-ranging comorbid mental health problems.