Waveforms for forming helical stents with opposing and/or alternating pitch angles along their lengths are disclosed. A wire is bent to form a waveform having a series of sinusoidal segments between a first end and a second end thereof. Each sinusoidal segment is longitudinally offset from its adjacent segment(s). Each waveform includes at least one sinusoidal segment having a first portion in which the amplitude between consecutive turns of the wire gradually increases and a longitudinally offset second portion in which the amplitude between consecutive turns of the wire gradually decreases. The waveform is wrapped from one end to the other about a mandrel to form the stent and depending on the arrangement of sinusoidal segments along the waveform may have opposing and/or alternating pitch angles along a section or an entire length of the stent.