In this paper a large database of midlatitude E region coherent backscatter, obtained with a 50 MHz Doppler system, is used to investigate the long-term variability in echo occurrence. The backscatter is found to be dominated by pronounced quasi-periodic variations with periods in the range from about 2 to 9 days that persist for time intervals from about 10 to maybe more than 20 days and have no relation to geomagnetic activity. The most commonly observed periods appear in two preferential bands, that is, the 2 to 3 day and the 4 to 6 day band. Using concurrent ionosonde data we find the variations in backscatter to be exactly in-phase with similar periodicities in the occurrence of relatively strong sporadic E layers. The present findings support the possibility that planetary waves are responsible for the observed long-term periodicities which indicates also a close relation between planetary waves and the well known, but not well understood, seasonal Es dependence. We suggest, the planetary wave option constitutes a new component into the research of midlatitude sporadic E layer formation and occurrence that needs to be considered and closely investigated. ¿ 1999 American Geophysical Union