Studies using retrospective self-report or proxies of nonsuicidal self-injury (NSSI) in the lab have shown that NSSI is often preceded by intense negative emotions and followed by a decrease in negative emotions/tension, suggesting an emotion regulation function of NSSI. To investigate this emotion regulation function of NSSI in a more ecologically valid way, we used experience sampling methods to examine the temporal relationship between NSSI behavior and emotional experiences throughout the day in 30 inpatients currently staying in psychiatric hospitals. Because NSSI is especially prevalent and severe in patients with a borderline personality disorder (BPD), we focused on patients with high levels of BPD symptomatology. Results confirmed that high levels of negative emotion prospectively predicted a higher probability of engaging in NSSI in the next time interval. However, the occurrence of NSSI itself was related to concurrent increases in negative emotion and decreases in positive emotion, and even prospectively predicted an increase in negative emotion in the consecutive time interval. These preliminary results show that on a time scale of hours, instead of resulting in emotional relief, NSSI seems to be associated with a further increase in negative emotionality, shedding light on the cyclic nature of NSSI. General Scientific Summary Nonsuicidal self-injury (NSSI) is often considered as serving an emotion regulation function, leading to the decrease of negative feelings. Here, we show that while NSSI is indeed preceded by elevated levels of negative emotionality, it is in fact followed by an increase, not a decrease, of negative emotion within the timespan of hours in inpatients with borderline personality disorder features, shedding light on the cyclic nature of NSSI.