There are some indices in which legalization of medical cannabis in the Republic of Serbia might be considered. The purpose of this research was to assess knowledge and attitudes towards medical cannabis in an urban adult population. This cross-sectional study was conducted in December 2015 and January 2016. A convenience sample of study participants comprised users of the Community Health Center. A total of 360 adults were invited to participate. Data were collected through an anonymous questionnaire. Most participants (77.1%) answered correctly that cancer was indicative of medical cannabis treatment, while the remaining conditions were less frequently recognized. A total of 42% answered correctly that adverse effects of cannabis were hallucinations and dizziness. Persons who previously used cannabis were more knowledgeable on conditions for medical cannabis treatment (ρ = 0.155; p = 0.006). Study respondents expressed positive attitude towards legalization of medical cannabis (median 5 out of 5) and negative towards legalization of recreational cannabis (median 2 out of 5). In conclusion, the adult population in Belgrade had some knowledge of medical cannabis. The overall attitude of our population regarding legalization of medical cannabis was positive, while the attitude towards legalization of cannabis for recreational purposes was negative.