1 INTRODUCTION  
2 OBSERVATIONAL DATA  
2.1 Sample selection  
2.2 Galactic Plane Surveys  
2.3 UKIRT/RMS K-band imaging  
3 SOURCE DETECTION  
3.1 Point source catalogues  
3.2 Completeness  
3.3 Physical binary probability  
3.4 Physical companions  
3.5 Mass ratios  
4 RESULTS & DISCUSSION  
4.1 Statistical differences in surveys and galactic regions  
4.2 Multiplicity statistics  
4.3 Mass ratios  
4.4 Are binary YSOs different from single YSOs?  
4.5 Total multiplicity  
5 CONCLUSIONS