This research undertook an assessment of Large Language Models (LLMs) within the domain of clinical diagnostics, specifically investigating their capacity to interpret symptom-centered inputs and generate precise clinical assessments. The investigation focused on evaluating several prominent architectures—including GPT-4, GPT-4o, Gemini, o1 Preview, and GPT-3.5—to gauge their proficiency in identifying clinical conditions solely from presented symptomatology. To guarantee clinical validity and appropriateness, symptom profiles were compiled from verified medical literature. Each architecture underwent testing within standardized environments to quantify diagnostic accuracy, precision, recall, and underlying logical processing. Specialized clinical scenarios were structured to examine performance boundaries across both routine and critical diagnostic conditions. The findings indicated that GPT-4 delivered the highest overall diagnostic accuracy, displaying a strong synergy with established medical logic. Conversely, Gemini demonstrated superior performance in high-stakes environments where exact decision-making is vital. Both GPT-4o and o1 Preview presented equitable metrics, maintaining a stable balance between precision and recall while managing real-time diagnostic scenarios. While possessing less advanced capabilities, GPT-3.5 remained functional for standard diagnostic duties. Ultimately, this investigation outlines the current capabilities and constraints of utilizing LLMs for clinical determination. Even though architectures like GPT-4 and Gemini show significant capability, critical barriers regarding data confidentiality, ethical protocols, and training bias correction must still be overcome. These insights offer strategic directions for the ethical incorporation of LLMs into diagnostic frameworks to optimize patient care outcomes.