Summary: The gcd-sum is an arithmetic function defined as the sum of the gcd's of the first n integers with n: $g(n) = sum_{i=1..n}$ (i, n). The function arises in deriving asymptotic estimates for a lattice point counting problem. The function is multiplicative, and has polynomial growth. Its Dirichlet series has a compact representation in terms of the Riemann zeta function. Asymptotic forms for values of partial sums of the Dirichlet series at real values are derived, including estimates for error terms.