This study investigated the effects of differing densities of glossing on the uptake of target words and the comprehension of idea units from a reading text. The focus was whether different densities of glossing would create trade-off effects. Thirty-three Malaysian ESL learners were assigned to three different conditions: high-density glossing, low-density glossing, and no-glossing. Three weeks after a vocabulary pretest the participants read a text under one of the conditions, and took a reading comprehension test and a vocabulary posttest. The results revealed that there were no trade-off effects between reading comprehension and uptake of the target words. However, the glossed words did appear to detract from the uptake of un-glossed vocabulary. The results also hinted at a trade-off effect between attention given to idea units containing glossed target words, and those that did not contain glosses. The findings suggested that teachers should be aware of potential side-effects of glossing.