Background: Lymphocytosis, characterized by an abnormal increase in circulating lymphocytes, poses diagnostic challenges due to its association with various underlying medical conditions. Peripheral smear examination remains a fundamental tool in identifying morphological clues indicative of specific aetiologies. Objective: This prospective study aimed to comprehensively assess lymphocyte morphology in adult patients with lymphocytosis, establish clinical correlations, and refine diagnostic approaches. Methods: Fifty-two adult patients with lymphocytosis were included, and clinical, haematological, and morphological data were collected. Peripheral blood smear examination, biochemical tests, and clinical follow-ups were conducted. Statistical analyses were performed to identify significant associations. Results: The study encompassed a broad age range, with middle-aged adults representing the largest group. Females were more represented than males. Majority of patients exhibited lymphocytosis with normal leukocyte counts. Neutrophilia was predominant, while thrombocytopenia was rare. Additional tests were conducted in a subset of patients, and lymphadenopathy was infrequent.