Grover disease (GD) is a rather common papular pruritic dermatosis that can be transient, persistent, or asymptomatic. The microscopic diagnosis of clinically suspected lesions can be challenging because GD can adopt different patterns, and involved areas are generally admitted to be mostly focal. The histopathologic hallmark of the disease is acantholysis, frequently combined with dyskeratosis, which confers the lesions an appearance similar to Darier disease, Hailey-Hailey disease, or pemphigus. Eczematous features can be observed as well. In this study of 120 consecutive cases of GD, we have found a sex and age incidence similar to what has been previously described, with no obvious seasonal influence, but careful evaluation of their microscopic features suggests that the histopathological diagnostic criteria of GD should be expanded. Specifically, in addition to the commonly described GD findings, we have detected cases with porokeratosis-like oblique columns of parakeratosis, lesions showing a nevoid or lentiginous silhouette, intraepidermal vesicular lesions, lichenoid changes with basal vacuolization and dyskeratosis, and dysmaturative foci with keratinocyte atypia. Moreover, quite often the dermal infiltrate was composed not only of lymphocytes intermingled with eosinophils, but also of neutrophils. In many cases, the capillary vessels showed hints of vascular damage including endothelial tumefaction due to cytoplasmatic edema and erythrocyte extravasation. Finally, because involved areas were larger than 2 mm in more than 50% of our cases, we should assume that GD lesions are not always as small as commonly claimed. Awareness of the patterns newly described herein may be important to avoid underdiagnosis of GD and may contribute to understand the pathogenesis of this acantholytic disease. © 2010 by Lippincott Williams & Wilkins.