Several studies have been made in the field of second language acquisition (SLA) regarding incidental vocabulary acquisition through reading. However, the majority have focused on the meaning of a word to measure complete acquisition. Nation (2001) argues that there are three main criteria for knowing a word, namely form, meaning and use, and it is not until all three criteria are met that one acquires new vocabulary. Therefore, we chose to create a study which focuses on incidental vocabulary acquisition through reading, but that focuses on three sub-criteria of Nation’s three main ones, namely recognition, association and collocation. In a previous study (Erlandsson and G. Wallgren 2017) we concluded that higher vocabulary knowledge contributes to better reading comprehension. Additionally, researchers (Horst et al. 1998; Day et al. 1991; Zahar et al. 2001; Waring and Takaki 2003; Pigada and Smith 2006, and Zhao et al. 2016) have also brought up several factors, such as learners’ prior proficiency level and word frequency, that can affect the outcome of incidental vocabulary acquisition. Therefore, we decided to investigate what impact these two factors have as well.  Our research questions are: How much vocabulary is learnt incidentally through reading, and how do proficiency and word frequency affect incidental vocabulary acquisition? These questions were answered through a study made in a classroom environment with students in the 8th grade. We were inspired by a study made by Waring and Takaki (2003) who focused on two main criteria for knowing a word, form and meaning. Our study was done through reading nine chapters from the novel Holes by Louis Sachar (2001) and to determine the degree to which rate word frequency played a part in incidental vocabulary acquisition, 24 words were chosen within four different ranges of word frequency (ranging between two occurrences to 39 occurrences in the text). These 24 words were then replaced with substitute words to ensure that each test word was new to the participants. First, the participants completed a reading comprehension test to establish the participants’ reading proficiency levels in English. They were later asked to read the chapters containing the substitute words. Directly after the reading exercise, the participants completed a vocabulary acquisition test. The vocabulary acquisition test consisted of three parts that focused on recognition (word recognition), association (multiple choice) and collocation (putting the target words in a context). Results show that words are acquired incidentally through reading. Our findings show a positive correlation between high reading proficiency levels and a higher amount of words acquired. The findings also indicate a positive correlation between words within a higher frequency range with a higher chance of being acquired. Furthermore, we also observed that substitute words with low frequency in some situations had a higher uptake than those words with a higher frequency. After this observation we tried to explain the anomaly by looking into the textual context of the surrounding words and found a potential explanation in the fact that the low frequency words had very descriptive surroundings.