INTRODUCTION: Alcohol use is a key risk factor for disease worldwide. Consumption of alcohol is increasing in sub Saharan Africa, where youth are already at high risk of HIV due to its high prevalence in the region. Studies show that youth begin drinking alcohol early; however, there is a need to further explore the initiation of alcohol use in order to design appropriate interventions in this population. METHODS: We conducted a qualitative study with youth in Mwanza and Kilimanjaro regions in Tanzania to explore alcohol consumption among youth. Participants were a purposive sample of youth aged 15-24 composed of secondary school and college students, and formal and informal sector employees. We conducted 35 in-depth interviews using a semi-structured guide to understand youth's personal experiences with alcohol consumption. Two social scientists conducted a multi stage, inductive analysis of the data. FINDINGS: Alcohol consumption was reported to mainly start during adolescence, although in some cases it started as early as at 10 years of age. Young women reported drinking less, and initiated drinking later compared to males. Social space assumed a primary role in alcohol initiation. The social environment and influence of important social actors were key aspects of youth's social space. Youth reported starting to consume alcohol at home, social events and in stressful environments with key influencers being parents, relatives, peers and intimate partners. CONCLUSIONS: Our findings show that the social space (social environment and interactions) plays an important role in influencing youth initial consumption of alcohol. Interventions addressing alcohol initiation among the population need to address the social spaces where initiation takes place and engage the significant actors in these spaces. There is need to further explore underlying societal drinking norms to better understand how they shape social environments and young people's initiation of alcohol use.