Context : New eclipse minimum timings of the M4.5/M4.5 binary CM Dra were obtained between the years 2000 and 2007 .
In combination with published timings going back to 1977 , a clear non-linearity in observed-minus-calculated ( O-C ) times has become apparent .
Several models are applied to explain the observed timing behavior .

Aims : Revealing the processes that cause the observed O-C behavior , and testing the evidence for a third body around the CM Dra system .

Methods : The O-C times of the system were fitted against several functions , representing different physical origins of the timing variations .

Results : An analysis using model-selection statistics gives about equal weight to a parabolic and to a sinusoidal fitting function .
Attraction from a third body , either at large distance in a quasi-constant constellation across the years of observations or from a body on a shorter orbit generating periodicities in O-C times is the most likely source of the observed O-C times .
The white dwarf GJ 630.1B , a proper motion companion of CM Dra , can however be rejected as the responsible third body .
Also , no further evidence of the short-periodic planet candidate described by Deeg et al .
( 2000 ) is found , whereas other mechanisms , such as period changes from stellar winds or Applegate ’ s mechanism can be rejected .

Conclusions : A third body , being either a few-Jupiter-mass object with a period of 18.5 \pm 4.5 years or an object in the mass range of 1.5 M _ { \mathrm { jup } } to 0.1 M _ { \sun } with periods of hundreds to thousands of years is the most likely origin of the observed minimum timing behavior .