Globally 320 million young people between ages 15-29 years are dying from alcohol related causes. Child line foundation survey report showed that 13.1% of the people involved in drug and substance abuse in India, are adolescents. India’s 1.2 billion populations contain the largest number of street children of the world who are at risk of substance abuse. But there is a gap in reliable data of adolescent substance abuse patterns in Assam as well as in India. Substance abuse pattern in the slums need more research. It was a community based cross sectional study. Study period was three months, from 15th July to 15th October 2012. Six slums of Guwahati city were selected purposively. Both male and female adolescents between the ages of 10-19 years with past or present history of any substance abuse, permanent residents of these slums, with guardian and self-consents given to take part in this study were included in the study. Each study subject was interviewed by personal interview method using a predesigned pretested Performa. Total 60 respondents, 20 from each of the selected slums were interviewed in detail. Male: Female ratio was 4:1, 93.3% were current abusers, maximum (46.7%) in the age group of 14-16 years. 58% were students and living with families (93%) though 30% of the respondents had single parenting. 25% of the respondents were illiterate and 93.3% were from lower socioeconomic status. 78.3% had history of drug abuse in their families and more than 2/3rd got information about the different substances from their peers and friends. Influence of friends/ peers (80%) and enjoyment or curiosity(73.4%) were prime reasons of starting the abuse. Majority (95%) adolescents obtained abusive substance from their peers /friends. Biddi (85%), gutkha( 88.3%), khaini (51.7%) and cheap branded alcohol(50%) were predominantly used. Chewing (90%) and smoking and inhalation (85%) were found to be the dominant routes of abuse. Substance abuse was rampant amongst school going males in the age group of 14-16 years initiated mostly in the age group of 8-13 years, majority with some members of the family involved with substance abuse and were from lower socio-economic strata. Tobacco and alcohol were mostly abused. Peers were found to be the major influencing factors of substance abuse initiation and supply source of the abused substances. Involvement in fights, vandalism and criminal activities were observed to be closely associated with the substance abuse behavior.