Oral examination alone cannot always distinguish benign from premalignant and malignant lesions, thereby resulting in delayed patient referral and poorer prognosis. Thus, any non-invasive technology which highlights oral premalignant and malignant lesions in a highly sensitive and specific manner will undoubtedly aid clinicians in early diagnosis and treatment of these conditions. The aim of this study was to assess the efficacy of acetic acid mouthwash and diffused light illumination (Microlux/DL) as a diagnostic aid in the visualisation of oral mucosal lesions and its ability to highlight malignant and potentially malignant lesions. Fifty patients referred for assessment of an oral white lesion were initially examined under routine incandescent operatory light. The location, size, ease of visibility, border distinctness and presence of satellite lesions were recorded. Clinical examination was repeated using the Microlux/DL diffused light illumination kit. An incisional biopsy was performed to provide a definitive histopathological diagnosis. Microlux/DL examination enhanced the visibility of 34 lesions, however, it did not help uncover any clinically undetected lesions, change the provisional diagnosis, or alter the biopsy site. Microlux/DL showed a sensitivity of 77.8% and a specificity of 70.7%, with a positive predictive value of 36.8%. Although Microlux/DL appears useful at enhancing lesion visibility, it is a poor discriminator for inflammatory, traumatic and malignant lesions.