We conducted two studies to test the validity, reliability, feasibility and acceptability of using video chat technology to quantify dietary and pill-taking (i.e. supplement and medication) adherence. In study 1, we investigated whether video chat technology can accurately quantify adherence to dietary and pill-taking interventions. Mock study participants ate food items and swallowed pills, while performing randomised scripted ‘cheating’ behaviours to mimic non-adherence. Monitoring was conducted in a cross-over design, with two monitors watching in-person and two watching remotely by Skype on a smartphone. For study 2, a twenty-two-item online survey was sent to a listserv with more than 20 000 unique email addresses of past and present study participants to assess the feasibility and acceptability of the technology. For the dietary adherence tests, monitors detected 86 % of non-adherent events (sensitivity) in-person v. 78 % of events via video chat monitoring (P=0·12), with comparable inter-rater agreement (0·88 v. 0·85; P=0·62). However, for pill-taking, non-adherence trended towards being more easily detected in-person than by video chat (77 v. 60 %; P=0·08), with non-significantly higher inter-rater agreement (0·85 v. 0·69; P=0·21). Survey results from study 2 (n 1076 respondents; ≥5 % response rate) indicated that 86·4 % of study participants had video chatting hardware, 73·3 % were comfortable using the technology and 79·8 % were willing to use it for clinical research. Given the capability of video chat technology to reduce participant burden and outperform other adherence monitoring methods such as dietary self-report and pill counts, video chatting is a novel and promising platform to quantify dietary and pill-taking adherence.