The existence and uniqueness of positions computed from Global Positioning System (GPS) pseudorange (PR) measurements is studied. Contrary to several recent claims [2, 3], in the case of n = 4 satellites a fix may not exist, and, if a fix exists, it is not guaranteed to be unique. In the case of n greater-than-or-equal-to 5 satellites a unique fix is assured, except in certain degenerate cases such as coplanar satellites. Finally, an alternate formulation of the direct n = 4 PR to three-space position solutions [2, 3] is presented, and simple tests for existence and uniqueness are derived.