Let B(n, q) be the class of block graphs on n vertices having all its blocks of size q + 1 with q ≥ 2. In this article we prove that the maximum spectral radius ρ(G), among all graphs G ∈ B(n, q), is reached at a unique graph. We profit from this fact to present an tight upper bound for ρ(G). We also prove that if G has at most three pairwise adjacent cut vertices then the minimum ρ(G) is attained at a unique graph. Likewise, we present a lower bound for ρ(G) when G ∈ B(n, q).