There is increasing concern among researchers about collecting data on sex and gender variables, yet many researchers are unsure of how to deal meaningfully with these variables. Drawing on literature that tests the psychometric properties of sex and gender demographic questions, we present considerations for collecting sex and gender demographic data. Extant literature suggests that asking asingle question to collect both sex and gender data contributes to nonresponse bias and the misclassification of asignificant proportion of gender minority participants. Aminimum of two questions, one asking sex assigned at birth and one asking gender identity, are recommended for the reduction of measurement error and the ethical treatment of gender minority individuals. We offer acritical discussion of options for these questions, with advantages and disadvantages of each approach. Clarifying demographic questions is crucial to methodological and ethical rigour of research engaging sex and gender data.