In light of the methodological and ethical issues associated with using a male/female tick box to collect gender data, researchers are increasingly questioning how to measure gender inclusively in survey research. Open-ended measures afford the greatest flexibility, though whether they are practical for large-scale surveys has yet to be tested. Here, we systematically assess the feasibility of open-ended gender measures drawing on a New Zealand national probability sample (New Zealand Attitudes and Values Study, N = 15,758). We asked participants "What is your gender?" as an open-ended measure of gender, and developed a simple, cost-effective coding scheme for coding qualitative gender data. Results indicate that very few participants (n = 15) self-identified as transgender, or outside of the male/female gender binary. Moreover, we find no evidence that implementation of the open-ended measure contributes to non-response rates or panel attrition. Taken together, these results demonstrate that large-scale surveys can feasibly implement inclusive measures of gender as an alternative to binary categorical measures. Because the single-measure approach likely underestimates the number of transgender participants, however, researchers interested in identifying all participants whose gender differs from their assigned sex should utilize two-step methods, which assess gender as well as assigned sex at birth.