ObjectiveTo systematically review and synthesise qualitative research exploring parents/carers’ experiences of seeking online information and support for long-term physical childhood conditions.DesignSystematic review and thematic synthesis of qualitative research.Data sourcesMedline, CINAHL, Embase, PsycINFO and the International Bibliography of the Social Sciences were searched from inception to September 2019. We used thematic synthesis to analyse findings.Eligibility criteriaPrimary research papers presenting qualitative data collection and analysis, focusing on parents/carers’ experiences of seeking health information and support from online resources for long-term physical childhood health conditions. No language restrictions were placed.Results23 studies from seven countries met inclusion criteria and were included in the synthesis. Included studies presented data collected through interviews/focus groups with 559 parents/carers; free-text surveys and essays with 26 parents/carers and 2407 messages from online support groups. Parents/carers developed a variety of strategies to obtain information and support online, based on personal preferences, appraisal of trustworthiness, perceived needs and previous experiences online. Many parents sought the benefits of online information and support, which included reassurance and validation from online communities, and feeling they had greater knowledge about their children’s conditions. Some concerns and perceived risks were discussed, which often stemmed from prior unsatisfactory experiences of seeking information and support online, consultations with health professionals and seeing distressing stories online.ConclusionMost parents/carers were successful in obtaining information and support online. Many continued to share experiences with other parents/carers online. The need for information was particularly apparent early after diagnosis of the condition, whereas the need for peer support continued. The potential concerns and perceived risks with information and support online were especially apparent among parents/carers of children with life-limiting long-term conditions. Findings may be useful for health professionals to facilitate discussions regarding use of online resources, and researchers designing online health resources for parents/carers.PROSPERO registration numberCRD42018096009.