Context :

Aims : Very young stellar clusters and cluster complexes may be embedded in dust lanes along spiral arms in disk galaxies and escape detection in visual bands .
Observations in the near-infrared K-band offer an almost unbiased view of such clusters or complexes due to the small attenuation by dust at this wavelength .
The objective is to determine their population size , absolute K-band magnitude distribution above the limiting magnitude imposed by the data , and location relative to the spiral pattern in disk galaxies .

Methods : All slightly extended sources were identified on deep K-band maps of 46 spiral galaxies reaching at least K=20.3 mag arcsec ^ { \mathrm { -2 } } at a signal-to-noise level of 3 .
The galaxies had inclination angles < 65 \degr and linear resolutions < 100 pc with seeing better than 1 \arcsec .
The sample includes both barred and normal spirals with a wide spread in types .
We also analyzed J- and H-band colors for 4 galaxies for which such images were available .
An apparent magnitude limit of K = 19 mag was used for the sources analyzed in order to avoid marginal detections .
Furthermore , we derived the source distributions of magnitudes and relative locations with respect to the spiral patterns .

Results : Almost 70 % ( 15/22 ) of the grand-design spiral galaxies show significant concentration of bright K-band knots in their arm regions corresponding to 30 % ( 15/46 ) of the full sample .
Color-color diagrams for the 4 spirals with JHK photometry suggest that a significant fraction of the diffuse sources found in the arms are complexes of young stellar clusters with ages < 10 Myr and reddened with several magnitudes of visual extinction .
The brightest knots reach an absolute K-band magnitude M _ { \mathrm { K } } of -15.5 mag corresponding to stellar clusters or complexes with total masses up to at least 10 ^ { 5 } M _ { \odot } .
Brightest magnitude and number of knots correlate with the total absolute magnitude of the host galaxy .
More knots are seen in galaxies with high far-infrared flux and strong two-armed spiral perturbations .
The bright knots constitute up to a few percent of the total K-band flux from their parent galaxy and account for a star formation rate of \sim 1 M _ { \odot } yr ^ { -1 } for the brightest grand-design spiral galaxies .

Conclusions :