Recently there has been much public discussion about children spending long afternoons alone at home. It has been claimed that spending a lot of time alone makes children vulnerable to many kinds of risk behaviour, such as smoking, use of alcohol and drugs, depression and poor school performance. Concerns have also been voiced about children’s unsupervised television watching, playing of computer games and surfing on the Internet. Yet, do we actually know how long the times are that children do spend alone at home and what do they do during that time? The purpose of this paper is to study how much time youngsters in Finland spend alone at home, who are the youngsters who are alone and what do they do when they are alone. The research data are data relating to households from the 1999–2000 Time Use Survey of Statistics Finland. The data cover the shared days of families with children on which all family members aged 10 or over kept a time use diary. The respondents recorded into the diaries at 10-minute accuracy whether they were alone or together with children aged under 10 belonging to the same household, other members of the household, or with other people they knew. Besides the data concerning being alone or together with somebody, the paper also exploits diary information on whether other members of the household were at home at the time in question. The scope of the study is limited to school students aged from 10 to 18. The material contains data on 191 schooldays and 229 days off school.