Background An increasing number of studies have used the diary method, which provides quantitative event-level data about sexual encounters. Diaries are an attractive tool for sexual behaviour research, yet little is known about the range of uses, methodological issues and best practices associated with this technology.

Objectives To conduct a systematic review of the literature regarding the use of web-based diaries in sexual risk behaviour studies.

Design Systematic review.

Data sources Five bibliographical databases, supplemented by references from previous reviews.

Methods Eligible studies were published in English before August 2013, used the internet to transmit data from collection device to study staff, and measured behaviours affecting HIV or sexually transmitted infection transmission risk. The primary author conducted an initial screen to eliminate irrelevant articles. Both authors conducted full-text reviews to determine final articles. We abstracted data on diary methodology, validity and reactivity (behaviour change caused by diary completion).

Results Twenty-three articles representing 15 studies were identified. Most diaries were collected daily for 1 month via websites, and completion was generally high (>80%). Compensation varied by study and was not associated with completion. Studies comparing diary with retrospective survey data demonstrated evidence of over-reporting on retrospective tools, except for the least frequent behaviours. Most studies that assessed reactivity as a result of diary completion demonstrated some change in behaviour associated with frequent monitoring.

Conclusions Web-based diaries are an effective means of studying sexual risk behaviour. More uniform reporting and further research on the extent of reactivity are needed.