The Internet offers a promising channel to conduct smoking cessation research. Among the advantages of Internet research are the ability to access large numbers of participants who might not otherwise participate in a cessation trial, and the ability to conduct research efficiently and cost‐effectively. To leverage the opportunity of the Internet in clinical research, it is necessary to establish that measures of known validity used in research trials are reliable when administered via the Internet. To date, no published studies examine the psychometric properties of measures administered via the Internet to assess smoking variables and psychosocial constructs related to cessation (e.g., stress, social support, quit methods). The purpose of the present study was to examine the reliability of measures of previous quit methods, perceived stress, depression, social support for cessation, smoking temptations, alcohol use, perceived health status, and income when administered via the Internet. Participants in the present study were enrolled in a randomized controlled trial of the efficacy of Internet smoking cessation. Following baseline telephone assessment and randomization into the parent trial, participants were recruited to the reliability substudy. An e‐mail was sent 2 days after the telephone assessment with a link to the Internet survey and instructions to complete the survey that day. Of the 297 individuals invited to participate, 213 completed the survey within 1 week. Results indicate that the internal consistency and test–retest reliability of the measures examined are comparable when self‐administered via the Internet or when interviewer‐administered via telephone.