Addiction to psychoactive substances is a serious problem, involved in a variety of social problems, such as crime, highway deaths, suicide, accidental deaths, hospitalization, poor school performance and dropout, job absenteeism, child and spouse abuse, low self-esteem, depression and anxiety. The purpose of this study is to investigate the significant relationship between substance use disorder (SUD) and ordinal birth order. Birth order is one of the seven major constructs in Individual Psychology and it has attracted the attention of many researchers. The sample is comprised of 166 subjects, recruited from both outpatient treatment facilities and the general population. Specifically, 51.2 % (n=85) were subjects with a history of substance use disorder and currently in remission/continuous abstinence from a primary drug usage.