Objectives To size human migration on the southern border between Colombia and Venezuela (Guainía department), and characterize the social, access and health care conditions relevant to the COVID-19 pandemic. Methods Mixed epidemiological and ethnographic study. Rate of Venezuelan migrants was calculated according to Migration Colombia data until December 31st, 2019, also effective access to medical care, and provision of health posts were calculated, with information from each Guainía health post collected from June 2017 to June 2019, through semi-structured interviews, participant observations, Google Earth™ and Wiki-loc™. Stata™ was used to calculate and graph median times of effective access. Cul-tural dynamics and health care conditions were described by the field work information and a permanent documentary review.Results Guainía is the 23rd department, according to the total number of Venezuelans, but the fourth in Venezuelans density (14,4%). In the Guainía river, the median times to the real reference health institution were 8,7 hours in winter and 12,3 in summer, and complex cases require air referrals. In the Inírida river, the median times to the real reference health institution were 11,9 hours in winter and 16,1 in summer. Only 57% of the health posts had supplies for acute respiratory infections. Conclusions Facing COVID-19 in south border territories, it is necessary to immediately strengthen medical and public health services to avoid high fatality rates. © 2020, Universidad Nacional de Colombia. All rights reserved.