AIM: Mental health first aid guidelines provide the public with consensus-based information about how to assist someone who is developing a mental illness or experiencing a mental health crisis. The aim of the current study was to evaluate the usefulness and impact of the guidelines on web users who download them. METHOD: Web users who downloaded the documents were invited to respond to an initial demographic questionnaire, then a follow up about how the documents had been used, their perceived usefulness, whether first-aid situations had been encountered and if these were influenced by the documents. RESULTS: Over 9.8 months, 706 web users responded to the initial questionnaire and 154 responded to the second. A majority reported downloading the document because their job involved contact with people with mental illness. Sixty-three web users reported providing first aid, 44 of whom reported that the person they were assisting had sought professional care as a result of their suggestion. Twenty-three web users reported seeking care themselves. A majority of those who provided first aid reported feeling that they had been successful in helping the person, that they had been able to assist in a way that was more knowledgeable, skilful and supportive, and that the guidelines had contributed to these outcomes. CONCLUSIONS: Information made freely available on the Internet, about how to provide mental health first aid to someone who is developing a mental health problem or experiencing a mental health crisis, is associated with more positive, empathic and successful helping behaviours.