A topical dermal delivery device, such as a patch, for topical delivery of nitric oxide (NO) to treatment sites of mammals is disclosed. The topical nitric oxide delivery device is provided for arrangement at a treatment site, and comprises a nitric oxide releasing fluid in use of said device, wherein said nitric oxide releasing fluid is at least partly liquid; a reservoir arranged to retain said nitric oxide releasing fluid; and a nitric oxide permeable layer adapted to adhere to said treatment site and adapted to provide an interfacial area for efficient transport of nitric oxide from said nitric oxide releasing fluid to said treatment site; wherein at least said nitric oxide permeable layer is geometrically flexible such that a loss of said interfacial area between said nitric oxide permeable layer and said treatment area is substantially avoided in use of said device, whereby said device is adapted to provide a desired, controllable and consistent delivery of said nitric oxide even under physical deformation of said device from said reservoir to said treatment site while avoiding transport of undesired species from said reservoir to said treatment site.