Objective: The study assessed suicidal ideation and interpersonal variables to explore the extent to which (a) changes in interpersonal factors predicted future suicidal ideation and (b) changes in either predicted nonsuicidal self-injury. Method: In total, 1,044 patients (72.3% Female; mean age = 41.95) at a psychiatric inpatient facility were assessed daily for suicidal thoughts. If patients indicated suicidal thinking (n = 417), their feelings of perceived burdensomeness and thwarted belongingness were assessed. Results: There was a reciprocal relationship between suicidal ideation and interpersonal factors, with both predicting each other on the next day. Changes in suicidal ideation, but not interpersonal factors, over two days were a significant predictor of 22.6% of nonsuicidal self-injury cases (n = 67). Conclusions: The findings reinforce the need for more intensive assessment of suicidal ideation (i.e., days, hours) to determine complex relationships with risk factors. This acts to enhance prediction and prevention of suicidal ideation and nonsuicidal self-injury.