“The ethical alignment of large language models (LLMs) in clinical decision making remains unclear, particularly their susceptibility to socio-demographic biases. We therefore tested whether LLMs shift medical ethical decisions in healthcare when presented with socio-demographic cues. Using 100 clinical vignettes, each posing a yes or no choice between two ethical principles, we compared the responses of nine open-source LLMs (Llama 3.3-70B, Llama 3.1-8B, Llama-3.1-Nemotron-70B, Gemma-2-27B, Gemma-2-9B, Phi-3.5-mini, Phi-3-medium, Qwen-2.5-72B, and Qwen-2.5-7B). Each scenario and modifier combination was repeated 10 times per model for a total of approximately 0.5 million experiments. All models changed their responses when introduced with socio-demographic details (p < 0.001). High-income modifiers increased utilitarian choices and decreased beneficence and nonmaleficence preferences, and marginalized-group modifiers raised autonomy considerations. Although some models demonstrated greater consistency than others, none maintained consistency across all scenarios, with the largest shifts observed in utilitarian choices. These results reveal that current LLMs can be steered by socio-demographic cues in ways not clinically justified, posing risks for equitable care in healthcare-informatics applications. This underscores the need for careful auditing and alignment strategies that ensure LLMs behave in ways consistent with widely accepted ethical principles while remaining attentive to the diversity, complexity, and contextual sensitivity required in real-world clinical practice.”