© 2018 Muri-Gama et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Background Being aware of consumption patterns of antimicrobials is the first step in designing and implementing strategies to change behaviors and, thus, to reduce the occurrence of antimicrobial resistance. The present survey was carried out to identify and describe the use of antimicrobials without prescription in riverside dwellers of the Brazilian Amazon Basin. Methods A cross-sectional study was carried out from a conglomerate stratified sample in the rural municipality of Coari, Amazonas State, Brazil, between April and July 2016. The survey was conducted in the riverside dwellers’ homes, and information was collected on all antimicrobials taken with and without medical or dental prescription for a 30-day period, together with indications of their use before the interview. Results A total of 492 riverside dwellers were included in the present survey; 346 (70.3%) had taken at least one medication during the previous month, and 74 (21.3% of those taking a medicine) used an antimicrobial. Two-thirds of the patients treated with an antimicrobial (49; 66.2%) obtained it without a prescription. Additionally, one-third of the antimicrobials consumed by the study sample (25) were used for non-infectious or non-bacterial conditions. Discussion The present survey showed not only that inappropriate use of antimicrobials is present in remote places such as the Amazon Basin, but also that one-third of those antimicrobials were taken to treat non-infectious or non-bacterial conditions. In addition to an unnecessary risk of adverse effects to the exposed populations, the inappropriate use of antibiotics without prescription helps to increase antibiotic-resistant strains. In the present case, this was happening near one of Latin America’s most important water supplies, which could contribute to the global impact of antimicrobial resistance.