Adolescent mental health research is a developing area. Inpatient units are the most widely used acute element of adolescent mental health services internationally. Little is known about inpatient units, particularly when it comes to measuring improvement for adolescents. Clinical outcome measurement in the broad context has gathered momentum in recent years, driven by the need to assess services. The measurement of outcomes for adolescents who access inpatient care is critical, as they are particularly vulnerable and are often considered the most difficult to treat. Following the PRISMA guidelines, the aim of this review was to assess whether adolescent inpatient units are effective and understand how outcomes are measured. CINAHL, MEDLINE with Full Text, ERIC, PsycINFO, and Cochrane databases were systematically searched. Studies were included if the inpatient units were generic and adolescents were between the mean age of 12-25 years. Furthermore, studies published in English within the last ten years were included. Exclusions were outpatient and disorder-specific inpatient settings. A total of 16 studies were identified. Each study demonstrated effectiveness on at least one outcome measure in terms of symptom stabilization. However, several outcome measures were used and therefore inpatient units lack consistency in how they measure improvement. Inpatient units are effective for the majority of young people as they result in symptom stabilization. Whilst symptom stabilization can be achieved, future research examining the mechanism of change is needed.