Radiosonde data obtained over the past 30 years from nine tropical stations have been analyzed to investigate the variability in height of the tropical tropopause on interannual time scales and on hemispheric spatial scales. A high degree of spatial coherence was found to exist among the stations, indicating that the tropical tropopause responds to large-scale driving forces as well as to local influences. The tropopause height was found to have a significant dependence on the phase of the quasi-biennial oscillation in the zonal winds of the tropical stratosphere and on the sea surface temperature anomalies of the tropical Pacific Ocean (the El Nino/Southern Oscillation phenomenon). A strong positive correlation between tropical tropopause heights and solar activity, reported earlier by several authors, is shown to have been transitory and possibly coincidental. The implications of these results are discussed. A comparison of tropopause height/temperature and height/saturation water vapor mixing ratio relationships at Yap ahnd Curacao is consistent with suggestions that the western tropical Pacific is an important source region for stratospheric water vapor.