Objective Communicating treatment risks and benefits to patients and their carers is central to clinical practice in modern healthcare. We investigated the challenges of risk communication by clinicians offering thrombolytic therapy for hyperacute stroke where treatment must be administered rapidly to maximise benefit. Method Semistructured interviews with 13 clinicians from three acute stroke units involved in decision making and/or information provision about thrombolysis. We report on clinicians' accounts of communicating risks and benefits to patients and carers. Framework analysis was employed. Results We identified the major challenges facing clinicians in communicating risk in this context that is, disease complexity, patients' capacity and time constraints, and communicating quality of life after stroke. We found significant variation in the data on risks and benefits that clinicians provide, and ways these were communicated to patients. Clinicians' communication strategies varied and included practices such as: a phased approach to communicating information, being responsive to the patient and family and documenting information they gave to patients. Conclusions Risk communication about thrombolysis involves complex uncertainties. We elucidate the challenges of effective risk communication in a hyperacute setting and identify the issues regarding variation in risk communication and the use of less effective formats for the communication of numerical risks and benefits. The paper identifies good practice, such as the phased transfer of information over the care pathway, and ways in which clinicians might be supported to overcome challenges. This includes standardised risk and benefit information alongside appropriate personalisation of risk communication. Effective risk communication in emergency settings requires presentation of high-quality data which is amenable to tailoring to individual patients' circumstances. It necessitates clinical skills development supported by personalised risk communication tools.