BACKGROUND: Dermoscopy is a helpful tool that can assist experienced users improve the diagnostic accuracy for pigmented lesions in acral sites. As a simplification, one can assume that if pigment is found predominantly in the furrows, the lesion can be considered benign, and if the pigmentation is present predominantly on the ridges, the lesion should be considered malignant. The differentiation between furrows and ridges is the main clue for the diagnosis, but this can sometimes be difficult to discern. For this reason, we describe a simple in vivo technique that makes this task much easier for the clinician. OBSERVATIONS: Liquid ink (ie, from a fountain pen) should be applied directly onto the lesion. The ink should be left on the skin for a few seconds to allow the ink to penetrate into the furrows. The excess ink should then be wiped off. The ink will at first diffusely color the entire skin surface. The subsequent cotton swab wiping will only remove the ink on the skin overlying the ridges. The furrows will retain the stain and become clearly visible on dermoscopic examination as thin inked lines. This in turn will make it easy to evaluate whether the melanin pigmentation follows the ink lines (benign pattern) or if the pigmentation is located in between these ink lines (malignant pattern). Conclusion The furrow ink test is a quick and easy method to facilitate the correct identification of furrows and ridges on volar skin and facilitates dermoscopic diagnosis of pigmented lesions in acral sites.