Introduction Molar-incisor hypomineralisation (MIH) affects one in six children in the UK. For the majority of patients who have mild MIH, this should be managed in primary care.Aims To assess UK-based general dental practitioners' (GDPs) ability to diagnose MIH when presented with multiple clinical vignettes.Design An electronic vignette survey was designed with use of clinical photographs - six cases had MIH and/or hypomineralised second primary molars (HSPMs) (seven possible diagnoses). Four control cases showing caries, fluorosis, amelogenesis imperfecta and dentinogenesis imperfecta were also included. Participants were UK-based GDPs. The survey was distributed by email and across social media platforms. Data collection occurred between February and May 2019.Results Seventy-six GDPs completed the survey; 68.4% (n = 52) of participants were female and 83% (n = 63) of participants graduated after the year 2000. The number of accurate diagnoses for each case were as follows - mild MIH (molars/incisors) 65.79%; mild MIH (molars only) 3.95%; HSPM and MIH (HSPM result) 0%; HSPM and MIH (MIH result) 50%; severe MIH (post-eruptive breakdown) 63.16%; severe MIH (caries) 31.58%; HSPM 3.95%.Conclusion GDPs are able to accurately diagnose MIH best when both incisors and molars are affected and caries is not present.