目標：描述私立西醫診所的執業規模、科別組合等變化，分析影響診所聯合執業的因素。 方法：利用1998年 (n＝8,544) 與2003年 (n＝8,571)「全民健康保險學術研究資料庫」，採用對數迴歸，分析地區人口數、競爭程度等因素對診所是否聯合執業的影響。 結果：臺灣私立西醫診所以單獨執業為主要型態，1998至2003年聯合執業的比例由17%增加至23%，且平均規模略為上升。控制其他變項之影響後，人口數愈多，65歲以上人口比例愈低，競爭程度愈高的地區，診所為聯合執業的機率愈高。骨科、耳鼻喉科、眼科等聯合執業的機率較高。 結論：診所執業型態的轉變可視為基層診所努力擴充資源、提升競爭力的表現，相較於一般基層醫師參與聯合執業意願調查結果，雖然高達62%醫師有意願參與聯合執業，真正付諸行動的卻佔少數，顯示聯合執業的實施仍有相當障礙。

Objective: To profile the practice modes of privately-owned clinics, in particular the average changes in scale and specialty mix, and to analyze factors associated with group practice. Methods: Data from the 1998 (n=8,544) and 2003 (n=8,571) National Health Insurance Research Database were used. Logistic regressions were used to examine whether local population and competition are significantly associated with establishment of group practice. Results: Single practice has been the major mode of practice in Taiwan. However, the proportion of group practice increased from 17% in 1998 to 23% in 2003, along with a slightly larger average scale. Controlling for other factors, greater population, younger population, and higher competition are positively and significantly associated with the probability of group practice. Specialties such as orthopedics, otolaryngology, and ophthalmology are more likely to form group practice than is general medicine. Conclusions: We consider the changes in practice modes as clinics' ways to expand resources and to gain an edge over competitors. Compared to documented willingness as high as 62% to participate in group practice, physicians in Taiwan have yet to transfer that willingness into action. Barriers to group practice still remain.