The concept of the appropriate adult (AA) was initiated in the United Kingdom in the 1985 Police and Criminal Evidence Act. An AA is an independent person who is called to the police station to assist and protect the rights and welfare of vulnerable suspects in police custody. A vulnerable person is any person under the age of 17 years and those adult suspects thought to be suffering from mental disorder or learning disability and considered at risk due to their limited understanding of their legal rights and their inability to understand the significance of questions asked or the implications. This study examined the effectiveness of the AA safeguard for vulnerable adult and juvenile suspects undergoing police interviews. It examined the records of suspects held in custody by the London Metropolitan Police at 74 charging stations during February 1997. Audio taped interviews were analyzed to obtain a general sense of the exchanges taking place. Of the 501 interviews analyzed, 365 were with adult suspects and 136 were with juveniles. The key characteristics of the interview, including length, number of officers present, status of the AA, and the presence of a legal representative (LR) were recorded. Overall, AA's made more than four times as many appropriate interventions than inappropriate ones. They contributed most often to satisfy the legal and procedural formalities of the interview. While the direct contribution of the AA in terms of what they say and do is quite limited, their presence during the interview appears to have a decisive effect on the behavior of the police and the LR. Additional analysis examined the effect of the presence and absence of an AA in adult and juvenile interviews. This is the first study that has examined in detail the contribution that the AA makes to the police-suspect interview process. Study limitations and implications are presented and discussed. References