Background People from South Asian backgrounds present to dementia services relatively late, often responding to crises. We aimed to devise and validate a theory of planned behaviour questionnaire to measure attitudes that predict medical help‐seeking for UK‐based South Asian people, to assess the effectiveness of future interventions promoting earlier help‐seeking. Methods We used focus groups to establish the content validity of culturally relevant questionnaire items, then asked participants to complete the questionnaire. We analysed reliability and validity and established the concurrent validity of questionnaire attitudes through correlation with willingness to seek help from a doctor for memory problems. We also correlated the scale with knowledge of dementia. Results The strongest predictor of willingness to seek help was perceived social pressure from significant others around help‐seeking; these attitudes were associated with beliefs about the views of family members and embarrassment around help‐seeking. Willingness to seek help was also strongly associated with attitudes about the benefits of seeing a doctor for memory problems, attitudes that were related to specific beliefs about what doctors can do to help. Attitudes in the questionnaire predicted 77% of variance in willingness to seek help, but no relationship was found with dementia knowledge. Conclusions We present the Attitudes of People from Ethnic Minorities to Help‐Seeking for Dementia (APEND) questionnaire, a valid and reliable measure of attitudes that influence help‐seeking for dementia in people from South Asian backgrounds, which could assess the impact of intervention studies. We suggest that interventions target attitudes specified here, rather than dementia knowledge. Copyright © 2016 John Wiley & Sons, Ltd.