Addressing the psychiatric aspects of serious illness in palliative care (PC) is crucial to both care delivery and outcomes. Psychiatric comorbidities are common among patients with PC needs and can significantly impact their total burden of symptomatic distress, overall quality of life, functional independence, and healthcare utilization. Yet, these aspects of care are often deferred to mental health consultant teams in the context of busy PC services and often limited human resources. To provide comprehensive and person-centered care, PC clinicians must understand the interplay between medical conditions and psychiatric presentations within a biopsychosocial framework to respond empathically, efficiently, and effectively. This article is the first of a two-part series developed in collaboration with a group of psychiatric-palliative care specialists. This article explores ten common physical manifestations of psychiatric illness and treatment among patients facing serious illnesses. The second article will provide pragmatic tips PC clinicians should know about the psychiatric manifestations of nonpsychiatric serious illness and treatment. Combined, these two articles support a holistic approach that PC clinicians can use to prioritize and integrate both mental and emotional well-being throughout the continuum of serious illness.