Street adolescents are exposed to many high‐risk behaviours such as drug abuse, risky sexual activity, violence and suicide. This issue is a challenge and concern in the health field in developing societies due to the lack of adequate welfare and support facilities. This study aimed to investigate high‐risk behaviours among street adolescents and the factors involved. This study was a cross‐sectional study of 124 street adolescents in Shiraz. Data were collected through four questionnaires: demographic information, Beck Scale for Suicidal Ideation (BSSI), Iranian Adolescents Risk Scale (IARS) and Russell Social Isolation Scale in the form of interviews. The highest mean risky behaviour in these participants was 17.07 ± 3.31 for sexual intercourse. The lowest risky behaviour observed in adolescents was high‐risk driving, averaging 8.21 ± 2.59. According to the results, 31.5 per cent showed a high risk of suicidal ideation. Also, 68.5 per cent of these adolescents reported a tendency to severe isolation. In general, street adolescents in Iran are highly vulnerable to high‐risk behaviours. This group of adolescents needs comprehensive support programmes from education centres, the Welfare Department and the Ministry of Health.