Starting from Lord (2008), who claims that ‘many researchers study the effects of L2 on mother tongue, but few researchers analyze the effects of mother tongue on L2’, I have decided to analyze in this piece of research the errors produced by Romanian students when translating tense-based sentences from Romanian into English, in order to establish whether or not the errors are produced as a consequence of the transfer of the grammar knowledge of the students from their mother tongue on L2 or, why not, if the errors occur as a result of other factors. It is often claimed that, when students transfer grammar knowledge from L1 into L2, errors may occur due to the structural grammar differences between the source and the target language. From this point of view, important differences between the Romanian and the English verb system (the aspect, the temporal sequentiality as reflected in posteriority, simultaneity and anteriority) might reveal in the end that Romanian students that learn English as a foreign language transfer in English structures and forms from Romanian, which inevitably leads to errors. When analyzing the reasons that lead to error making when learning a foreign language, linguists, didacticians and methodologists claim that the interference between the mother tongue (Romanian, in this case) and the newly learnt language (English) is an important source for making errors. Linguistic interference, also known as language transfer, refers to the transfer of linguistic features between languages, emphasizing the fact that the transfer can be either positive or negative. Positive linguistic transfer (target-like use of L2) is when the grammatical structure or element is the same in both languages and consequently, the produced outcome is correct. On the contrary, negative linguistic transfer (non-target-like use of L2) is when the grammatical structure is different from one language to the other and the outcome breaks the linguistic laws in the target language. The theoretical approach that deals with the analysis of the differences and similarities between languages is contrastive analysis which has demonstrated that when two languages are more distinct, the likelihood of greater negative transfer is all too possible. That implies that any two languages which have more similar grammatical rules would expectedly result in positive transfer. Contrastive analysis proves its usefulness especially in the teaching-learning process; firstly, the teacher must be aware of the differences between the students’ first language and their L2 in order to help students overcome difficulties when learning a foreign language and to reduce the number of transfer errors that students might produce. Secondly, the students need to become themselves aware of these differences so that they make fully-informed linguistic decisions. Thus, this is a predictive method of knowing beforehand what might lead to errors when Romanian students translate from Romanian into English. Nevertheless, teaching should not be based on this comparative analysis as the only way of teaching students.