Objectives: Considering the importance of demographic factors such as age, sex, education, type of abused substance, method of abuse, the effect of previous treatments and the severity of addiction on craving and subsequent successful treatment, this research was carried out with the aim of examining the relationship between these factors and the severity of craving in intravenous heroin addicts. Method: In this study 26 male heroin addicts were selected using snowball sampling from among abusing addicts not seeking treatment, in the city of Tehran, Iran. The subjects entered the study after a primary interview and completed a demographic and Addiction Severity Index (ASI). Thereafter, the severity of cravings were assessed and the subjects were divided into two groups of responders and non-responders to craving symptoms. Results: The responders were subjects with lower age, lower addiction durations, higher drug expenditure, higher withdrawal symptoms, and more severe addiction symptoms in many components of ASI. Also, age and education had a negative significant correlation and duration of abuse, daily cost of abuse and sub-components of substances, and legal and psychiatric problems had a significant correlation with individual reports of craving. Conclusion: Some demographic factors can be important predictors of craving in addicts, which is itself a considerable aspect of deviation from treatment. The independent positive significant effects of factors of craving and addiction severity in the linear regression model indicates a reciprocal relationship between substance abuse and craving. The independent negative significant effect of substance abuse duration in the linear regression model in this study can indicate the process of the development of an compulsive behavior from an impulsive behavior in the process of addiction development.