Context : Current atmospheric models can not reproduce some of the characteristics of the transition between the L dwarfs with cloudy atmospheres and the T dwarfs with dust-depleted photospheres .
It has been proposed that a majority of the L/T transition brown dwarfs could actually be a combinaison of a cloudy L dwarf and a clear T dwarf .
Indeed binarity seems to occur more frequently among L/T transition brown dwarfs .

Aims : We aim to refine the statistical significance of the seemingly higher frequency of binaries .
Co-eval binaries would also be interesting test-beds for evolutionary models .

Methods : We obtained high-resolution imaging for six mid-L to late-T dwarfs , with photometric distances between 8 and 33 pc , using the adaptive optics systems NACO at the VLT , and the Lick system , both with the laser guide star .

Results : We resolve none of our targets .
Combining our data with published results , we obtain a frequency of resolved L/T transition brown dwarfs of 31 ^ { +21 } _ { -15 } % , compared to 21 ^ { +10 } _ { -7 } % and 14 ^ { +14 } _ { -7 } % for mid-L and T dwarfs ( 90 % of confidence level ) .
These fractions do not significantly support , nor contradict , the hypothesis of a larger binary fraction in the L/T transition .
None of our targets has companions with effective temperatures as low as 360–1000 K at separations larger than 0 \aas@@fstack { \prime \prime } 5 .

Conclusions :