We present a statistical analysis of a complete sample (255) of northern planetary nebulae (PNe). Our analysis is based on morphology as a main parameter. The major morphological classes are: round (26&#37 of the sample), elliptical (61&#37), and bipolar (13&#37) PNe. About a half of the round and 30 &#37 of the elliptical PNe present multiple shells. Round PNe have higher galactic latitude (|b| = 12) and galactic height (< z > = 753 pc), than the elliptical PNe (|b| = 7, < z > = 308 pc) and bipolar PNe (|b| = 3, < z > = 179 pc). This possibly implies a different progenitor mass range across morphology, as a different stellar population would suggest.