In this paper we study the possible Picard numbers ρ of an abelian variety A of dimension g. It is well known that this satisfies the inequality 1 ≤ ρ ≤ g 2 . We prove that the set R g of realizable Picard numbers of abelian varieties of dimension g is not complete for every g ≥ 3, namely that R g [1, g 2 ] ∩ N. Moreover, we study the structure of R g as g → +∞, and from that we deduce a structure theorem for abelian varieties of large Picard number. In contrast to the non-completeness of any of the sets R g for g ≥ 3, we also show that the Picard numbers of abelian varieties are asymptotically complete, i.e. lim g→+∞ #R g /g 2 = 1. As a byproduct, we deduce a structure theorem for abelian varieties of large Picard number. Finally we show that all realizable Picard numbers in R g can be obtained by an abelian variety defined over a number field.