Abstract: A tamper-proof package having a plurality of interacting parts on a container neck and closure which form a pair of cylindrical facing surfaces. Cooperating sets of grooves and groove-engaging frangible male members, preferably splines, are on the facing surfaces. The container has a notched flange and the closure has corresponding lugs to engage the flange. Some of the lugs are preferably frangibly connected to the closure. Observation of the splines, the lugs, and the manner of opening provide indications of tampering or the absence thereof, even though the cooperating features are shielded between the closure and the container neck.