The present dataset, syntax and output are connected to a paper with the same name published in Journal of Social and Clinical Psychology (https://doi.org/10.1521/jscp.2025.44.3.203). This paper contains detailed information about how we processed data, sample characteristics and results from the analyses. This dataset contains: 1) SPSS data for this paper (Data PROCESSED ANON 23062026.sav), 2) Syntax of the descriptive analyses (e.g. sample characteristics, reliabilities, correlations) and the main analyses (regression analyses) including assumption checks (Syntax Descriptives and Main Analyses), 3) Output of all analyses (Output Descriptives and Main Analyses, OUTPUT AS PDF) and 4) The information page, informed consent form and survey (PDF of survey). ABSTRACT: Introduction: Adult attachment is theorized to affect psychological adaptation to bereavement. Attachment anxiety and attachment avoidance relate positively to grief levels concurrently. Yet, controlled longitudinal studies do not find that these attachment dimensions predict changes in grief levels. Therefore, we aimed to test the hypotheses that stronger lingering attachment to the deceased and lower use of living others to fulfill attachment-related needs longitudinally predict increased grief levels. Methods: A sample of 356 bereaved adults (84% women) completed a baseline survey assessing sociodemographic and loss-related characteristics, attachment anxiety, attachment avoidance, lingering attachment, use of living others for attachment needs, and grief levels. Additionally, 188 participants completed a measure of grief levels at 2-month follow-up. Results: Zero-order correlation analyses showed that stronger attachment anxiety, attachment avoidance, and lingering attachment related to higher grief levels concurrently and longitudinally, whereas the use of living others for attachment needs only related negatively to grief levels concurrently. Multiple regression analyses demonstrated that attachment anxiety and lingering attachment predicted higher future grief levels, over and above baseline grief levels. Discussion: Findings support a role of attachment anxiety and lingering attachment in adaptation to loss. Developing therapeutic techniques to reduce lingering attachment to the deceased might improve grief therapies.