As user experience studies move from laboratories to mobile context, we need tools for collecting data in natural settings. Based on the results from a pilot study, we present early guidelines for designing mobile questionnaires to be filled in on handheld, palm-sized mobile devices. We found that special attention needs to be paid to the clarity and simplicity of the structure, layout and questionnaire content, including questions, visual icons, items and scales. In addition to the requirements set by the screen size, also data entry method, interaction style and mobile context related issues need to be taken into account when designing questionnaires for mobile devices. Keywords Mobile devices, questionnaires, user experience, field study, evaluation, experience sampling ACM Classification Keywords H5.2 [User Interfaces]: Evaluation/methodology General Terms Experimentation, Measurement, Human Factors