The paper deals with singular first order Hamiltonian systems of the formwhere J ∈ R 2×2 defines the standard symplectic structure in R 2 , and the Hamiltonian H is of N -vortex type:This is defined on the configuration space {(z 1 , . . . , z N ) ∈ Ω 2N : z j = z k for j = k} of N different points in the domain Ω ⊂ R 2 . The function F : Ω N → R may have additional singularities near the boundary of Ω N . We prove the existence of a global continuum of periodic solutions z(t) = (z 1 (t), . . . , z N (t)) ∈ Ω N that emanates, after introducing a suitable singular limit scaling, from a relative equilibrium Z(t) ∈ R 2N of the N -vortex problem in the whole plane (where F = 0). Examples for Z include Thomson's vortex configurations, or equilateral triangle solutions. The domain Ω need not be simply connected. A special feature is that the associated action integral is not defined on an open subset of the space of 2π-periodic H 1/2 functions, the natural form domain for first order Hamiltonian systems. This is a consequence of the singular character of the Hamiltonian. Our main tool in the proof is a degree for S 1 -equivariant gradient maps that we adapt to this class of potential operators.MSC 2010: Primary: 37J45; Secondary: 37N10, 76B47