The authors present three cases of urticaria pigmentosa (UP), one with a very early beginning and two with a late beginning. The clinical symptoms orient the diagnosis of the three cases in relation to maculopapular exanthema of a dark pink color, brown macules and, in all cases, the presence of Darier's sign. As normal, the clinical diagnosis was confirmed by the histopathological examination of the skin. The evolution of the three patients was favorable in all cases, with the disappearance of symptoms in one case. In the other two cases the process is stabilized, and at no time have systemic manifestations been found. The relative rareness of UP in infancy, an expression of a proliferation of the reticuloendothelial system (RES) on a mast cell level with different evolutional possibilities, has been the justifying factor in the presentation of these new cases.