We consider a model for periodic patterns of charges constrained over a cylindrical surface. In particular we focus on patterns of chiral helices, achiral rings or vertical lamellae, with the constraint of global electroneutrality. We study the dependence of the patterns' size and pitch angle on the radius of the cylinder and salt concentration. We obtain a phase diagram by using numerical and analytic techniques. For pure Coulomb interactions, we find a ring phase for small radii and a chiral helical phase for large radii. At a critical salt concentration, the characteristic domain size diverges, resulting in macroscopic phase segregation of the components and restoring chiral symmetry. We discuss possible consequences and generalizations of our model. [7,8]. A considerable aspect of these systems is the presence of surface charge heterogeneities or domains [9,10], which arises from the competition of electrostatic forces with segregating forces such as steric, van der Waals, and hydrogen bonding interactions. These surface patterns have been shown to be important for the stability and functionality of the aggregates [2,11,12,13].A key feature in many biological processes is pattern recognition and specificity within isomeric aggregates [14]. Biomolecules exploit repetitive patterning over surfaces, which often breaks some underlying symmetry, in order to increase their functionality [15]. In this context, chiral symmetry (that is the absence of improper rotation axis) is notably interesting: although its role in chemistry and biology is widely recognized [2,16,17,18], its origin in biology is the subject of much debate [19]. Many systems are chiral due to the chirality of its components [19,20]. For instance, colloidal solutions of rodlike viruses provide an intriguing example of chiral structures in liquid crystalline phases [21]. Nevertheless, understanding whether electrostatic interactions alone are capable of producing chiral systems would shed further light on the issue.From a theoretical vantage point, the electrostatic patterning of a system of charges on cylindrical surfaces is however relatively unexplored. Certainly, the effects of long-range electrostatic forces have been widely studied for planar two dimensional systems [22]; also the behavior of short-range interactions over cylindrical geometries has been addressed, such as the Ising model on the cylinder [23]. We analyze here an intermediate case where charges are confined over a cylindrical surface and interact via long-range forces. A further issue we consider is whether spherically symmetric electrostatic interactions are capable to break translational, rotational or chiral isometries of the cylinder. Recently, there has been interest to study crystalline systems over constrained geometries such as the surface of spheres, cylinders, and tori [24,25,26]. The generalization to more general curved substrates shows an interesting rich behavior [27].In this Letter we provide the full phase diagram of lamellar charged patterns on a cylinder, as a...