Primary hyperparathyroidism (PHPT) was previously considered a disease presenting with multiorgan involvement and a wide range of symptoms. Today, the disease presents with no symptoms or mild symptomatology in most patients. Data regarding nonspecific symptoms such as pain, fatigue, memory loss, depression, and other neuropsychiatric signs have been ambiguous, and results from prospective long‐term randomized control trials are lacking. The Scandinavian Investigation on Primary Hyperparathyroidism (SIPH) is a prospective randomized controlled trial (RCT) with 10‐year follow up, comparing parathyroidectomy (PTX) to observation without any treatment (OBS). From 1998 to 2005, 191 patients with mild PHPT were included from Sweden, Norway, and Denmark. A total of 95 patients were randomized to PTX and 96 to OBS. The generic Short Form‐36 survey (SF‐36) and the Comprehensive Psychopathological Rating Scale (CPRS) were studied at baseline, 2, 5, and 10 years after randomization. After 10 years, the PTX group scored significantly better on vitality (PTX 65.1 ± 20.2 versus OBS 57.4 ± 22.7;​ p = .017) compared to the OBS group in SF‐36. We found no differences between the groups in the physical subscales. The OBS group had no significant change in any of the SF‐36 scores throughout the study. The CPRS showed an improvement of symptoms in both groups for single items and sum scores after 10 years compared to baseline. There were, however, no significant differences between the two groups in the CPRS data. The results of this large and long‐term RCT indicate improvement in some of the mental domains of SF‐36 following PTX. However, the treatment effects between the groups were subtle with uncertain clinical significance. The observation group had stable SF‐36 values and improvement in CPRS symptom‐scores. Thus, in considering only quality of life (QoL) and in the absence of declines in renal and skeletal parameters, it may be safe to observe patients with mild PHPT for a decade.