Aims. The aims were to investigate potential effects of mode of administration on response rate, internal consistency, completeness of data, floor and ceiling effects and interaction effects of mode of administration, gender and age on self-reported health status and emotional distress among Swedish adolescents and young adults. Design. A cross-sectional comparative study. Methods. Using a stratified quota sampling scheme, 840 adolescents and young adults (aged 13-23 years) were randomly chosen from the general population. Participants were randomised according to mode of administration, telephone interview or postal questionnaire. Results. The telephone mode resulted in a higher response rate than the postal mode and fewer men than women participated in the postal mode. Mode of administration only had a small effect on self-reports. The youngest adolescents did, in some respects, respond to the modes in a reverse pattern than the older participants. Conclusion. The findings support the use of the SF-36 and the HADS among persons 16-23 years of age. The strengths and weaknesses of a telephone and a postal mode to collect self-report data are discussed. Relevance for clinical practice. Nurses should consider the findings of this study, e.g. when using self-reports to screen for health status and emotional distress and when designing research studies.