There are several apparently disparate conditions of the ureter for which there is little agreement about the cause. They have much in common, in that they all can be explained by variations in ureteric muscle development, with or without mucosal involvement. The functional significance of these conditions varies; lateral spurs and ureteric rings have no functional significance; ureteric valves produce a purely mechanical obstruction. Primary megaureter is of only functional significance, whereas PUJ obstruction is probably initially a functional obstruction with a mechanical obstruction developing subsequently (Table 1). A brief review of the current understanding of these interesting conditions, including some relevant embryology and physiology, should help to clarify their cause and justify their being grouped together as ‘congenital variations in mucomuscular development’.