Background: Adhesions after endometriosis resection are frequent and the most common causes for chronic pain and secondary infertility. Primary results of our randomized controlled trial (RCT) on adhesion prevention after deep infiltrating endometriosis (DIE) resection using the gel barrier 4DryField® PH showed 85% adhesion reduction in second-look surgeries. Secondary endpoint data on fertility and pain development were collected during 12-month follow-ups. Methods: This RCT comprised 50 patients. Preoperatively and after 1, 6 and 12 months, pain scores for cycle-independent pelvic pain, dysmenorrhea, dyspareunia, dyschezia, and dysuria, as well as the number of pregnancies, were recorded,. Results: The pregnancy rate in the intervention group was significantly higher (p < 0.05). Pain development was also improved: after 12 months, all 5 subscores were lower in the intervention group and improvements were more pronounced, most prominently concerning cycle-independent pelvic pain and dysmenorrhea, the two subcategories with the highest preoperative scores and, therefore, the highest relevance for the patients. Cycle-independent pelvic pain even recurred in the control group, while barrier application prevented this. Conclusions: Considering the known causal link between adhesions and pain, it is apparent that the favourable outcomes in the intervention group are linked to effective adhesion prevention. The significant increase in pregnancies is remarkable.