OBJECTIVES This study explores surrogate decision-makers' (SDMs) challenges making decisions related to the care of patients in critical care, to (1) characterise the SDM stress, (2) identify personal, social, care-related factors influencing stress and (3) consider implications of findings to improving critical care practice. METHODOLOGY Semi-structured interviews were conducted with SDMs of critically ill patients receiving care in two tertiary care institutions. Transcripts were analysed using a grounded theory approach. Domains explored were: stress characteristics, stress mitigators, coping strategies, social networks, SDM decision-making role, decision-making concordance, knowledge of patient's preferences, experience with provider team, SDM-provider communication, patient outcome certainty. MAIN OUTCOMES We interviewed 34 SDMs. Most were female and described long-term relationships with patients. SDMs described the strain of uncertain outcomes and decision-making without clear, consistent information from providers. Decision-making anxiety was buffered by SDMs' active engagement of social networks, faith and access to clear communication from providers. CONCLUSION Stress is a very real factor influencing SDMs confidence and comfort making decisions. These findings suggest that stress can be minimised by improving communication between SDMs and medical providers. Nurses' central role in the ICU makes them uniquely poised to spearhead interventions to improve provider-SDM communication and reduce SDM decision-making anxiety.